To recall, Jaysh Khalid ibn al-Waleed ('The Army of Khalid ibn al-Waleed') is an Islamic State-linked group in southwest Deraa province (the Yarmouk Valley/Basin area) on the border with the Golan Heights. Formed in late May 2016 mainly out of a merger of three groups, the most important of which was Liwa Shuhada' al-Yarmouk , Jaysh Khalid ibn al-Waleed came under the leadership of one Abu Hashim al-Shami, a man originally from Idlib province dispatched by the Islamic State to head the group. This followed on from the appointment of the Saudi Abu Abdullah al-Madani as head of Liwa Shuhada' al-Yarmouk in March 2016, a surprise appointment at the time that also had the hand of Islamic State involvement.
Though the above information is correct, it should be noted that the issue of leaders and their names has not been publicised on the official media channels of Liwa Shuhada' al-Yarmouk and the successor Jaysh Khalid ibn al-Waleed. Instead, fake and/or unofficial announcements publicising this correct information sometimes appear. Since the formation of Jaysh Khalid ibn al-Waleed, the links with the Islamic State have been made more obvious through consistent advertisement of Jaysh Khalid ibn al-Waleed releases on Islamic State media aggregate channels like Nashir News on Telegram (in fact, Telegram is currently the only outlet where official Jaysh Khalid ibn al-Waleed media exists). In addition, the Islamic State's auxiliary media wing Amaq News reports on developments concerning the group and the Yarmouk Valley area.
While the military situation is locked in a stalemate as the rebel factions supported by Jordan and the West find it difficult to penetrate the Yarmouk Basin and are largely not local to the area, Abu Hashim al-Shami (often referred to in local media as 'Abu Othman al-Idlibi', presumably based on his Idlib origins) was assassinated by the rebels. Though I have been able to confirm this information through private contact, a fake statement in the name of Jaysh Khalid ibn al-Waleed (below) was circulated regarding his death. Its lack of authenticity is demonstrated by its lack of appearance on Islamic State outlets like Nashir News on Telegram. In addition, the Jaysh Khalid ibn al-Waleed media account 'Mohammad Daraa' on Facebook (an account overseen by multiple people in Jaysh Khalid ibn al-Waleed media) decried the statement as a forgery (also below).
The pro-rebel outlet All4Syria has a report about the new amir to succeed Abu Hashim al-Shami. I have translated the relevant parts below. The appointment itself, which I have checked with a local source from Shajra who supports Jaysh Khalid ibn al-Waleed, appears to be genuine. This source says that this new amir, from the inhabitants of al-Hajr al-Aswad in the Damascus area (presently controlled by the Islamic State), came from the north of Syria (i.e. dispatched by the Islamic State from territory to the north of Jaysh Khalid ibn al-Waleed's holdings) and that he came with Abu Hashim. The source adds that this new amir previously worked as a security official (amni) in Jaysh Khalid ibn al-Waleed.
"All4Syria has learnt from a private source in the Yarmouk Valley area in west Deraa countryside, that Jaysh Khalid ibn al-Waleed, accused of allegiance to the Da'esh organization, has appointed a new leader for itself, following the explosion that targeted the car of the previous leader for Jaysh Khalid ibn al-Waleed Abu Hashim al-Idlibi last Tuesday on 18 October in the Yarmouk Valley area.
According to the source, the new leader for Jaysh Khalid ibn al-Waleed is Abu Muhammad al-Maqdisi, a former Shari'i in Harakat al-Muthanna that is considered among the most prominent formations that established Jaysh Khalid.
The source pointed out that Maqdisi is a Palestinian-Syrian who departed in 2014 towards the north of Syria, and joined the Da'esh organization. At the start of the present year, he returned to the south of Syria and worked within what is known as Wilayat Dimashq [Damascus province], and he continued thus until the date his appointment as leader for Jaysh Khalid days ago."
Overall, the assassination of Abu Hashim and appointment of a new leader will probably not change the situation. The military situation is at a stalemate and the question of who is the overall leader of Jaysh Khalid ibn al-Waleed seems to be of little relevance. After all, the Islamic State can simply dispatch another individual to replace the one who is killed. Indeed, although the Yarmouk Valley area is said to be under siege by the rebels and there is a real humanitarian impact, it is still possible for some people, goods and weapons to move in and out of the area. After all, Harakat al-Muthanna's leader Abu Ayyub al-Masalama departed the Yarmouk Valley earlier in the summer.
Update (27 October 2016): While I stand by the assessment that the overall military stalemate is not likely to change for now, the assassination of Abu Hashim al-Shami does raise questions as to whether the operation was an inside job. Some rumours hint that the assassination may have been the work of someone/people from the small Harakat al-Muthanna contingent that is in Jaysh Khalid bin al-Waleed. As I have noted in a previous post, Harakat al-Muthanna seems to have had problems integrating into the merger initiative. For example, note this post from Facebook:
"They kill the one killed and proceed in his funeral. After they undertook the assassination operation against the general amir for Jaysh Khalid bin al-Waleed- the Da'esh organization- and despite the fact that the suspicions are revolving around the Hisba official Abu Obeida al-Sa'adi [NB: he was originally in Harakat al-Muthanna], Shubat, Abu Hamza al-Amni and others, they are nonetheless arresting people so as to fabricate theatrics of discovery and attach the accusation on persons who have nothing to do with the matter, forcing them to confess under torture. This is so despite the fact that the matter was uncovered when it was executed at some metres away from the Saryat al-Hawin that is a security centre for them. And no one can approach this place, and those who possesses the information about the movements of the amir: it is only they themselves. And all know that their claimed amir tried to get near to the people and win affection of the people, and he tried to get near to the people on the grounds of resolving their problems, but he clashed with the men of the Hisba and the security officials. And these people have no popular support and thus interests conflicted, and so the men of the Hisba and the security officials worked to assassinate him because he began posing a danger to them and their interests."
Commenting on this post, one of the users writes: "The operation is greater than this. al-Muthanna and Shuhada' [al-Yarmouk] are soon going to slaughter each other because confidence has been lacking among them." Other posters (clearly pro-Jaysh Khalid and trying to downplay suggestions of internal problems) decry him as a liar, while another pro-Jaysh Khalid poster writes: "You seem to think that the Dawla [Islamic State] is like the Bashar regime. One branch doesn't like another. But you know that the problem the Islamic State in Hawdh al-Yarmouk is facing is that most of the people here like Bashar al-Assad. And you are the first of them. And by God's permission the Islamic State will trample on all the followers of the regime and the Sahwa forces, and remaining despite your haughtiness, oh enemies of God."
My source from Shajra, however, says to me: "[The post] is not strange. The one who killed the amir Abu Hashim is from within the group, and God knows best. The verification taking place will uncover it by God's permission. It is true the place of the crime is exclusively amni [i.e. only accessible to security personnel in the organization]. Whoever undertook it is from the members of Harakat al-Muthanna, though I rule out Abu Obeida."
Another source, originally from Zayzan in south Deraa countryside and a former supporter of Liwa Shuhada' al-Yarmouk, also says that there have been problems regarding Harakat al-Muthanna's presence within Jaysh Khalid ibn al-Waleed: "There are stories and rumours. There is disagreement. I also heard that members of al-Muthanna assassinated the amir Abu Hashim."