I'm calling it right now -- unless the UFC pays Islam a shitload of money under the table, I don't think this fight happens.
Guys like Islam and Khabib don't respond to blackmail/threats. I think the UFC is trying a power play to give Islam an ultimatum to defend against Topuria @ UFC 317 or vacate the title. However, they will be hard pressed to carry through on that threat. Islam can just say "I have injuries I need to heal, and I can't fight until October." What are the UFC going to do? They can't just strip him while they refused to strip Jon Jones of the title.
Best case scenario for the UFC is that Belal loses to JDM @ welterweight, and Islam decides to move up and fight JDM. Then Islam might consider vacating the belt if he's moving divisions. Otherwise, I think the UFC is screwed. Islam's camp want to fight Arman @ 155 (the #1 contender), to honor the integrity of the 155 belt and not fight yet another 145er. They aren't going to agree to fight Topuria on short notice at UFC 317.