This was the last city of note that ISIS held. After this their remaining strongholds would naturally drop quicker - but it is starting to look like ISIS going to stop fighting to the death, and run for it. Relatively large numbers have begun to surrender.
Deir ez Zour is almost as big as Raqqa was (~200K before the war), but is already surrounded and partially liberated by the Russians/Syrians/Iranians. There is nothing much left after that would hold a population over 50,000 - basically Mayadin and abu Kamal, and then just a bunch or rural villages/hamlets.
ISIS has taken so many losses of fighters, and lost so many leaders at so many levels, that they should be coming apart. Virtually no replacements are coming for ISIS. Their oil revenues and taxes are gone, they cut off from Turkey for re-supply and running out of ammo.
Full collapse could come at any time, but over this Winter is most likely, even if the fight to the last.
Some rump will remain, as well as their brand name, to form some undercover terrorist/guerrilla group - but the Caliphate is in its death throes.
Great news. THAT caliphate is dead but we still have to contend with the growing one in Turkey.