Everything you stated is plausible.
But I can easily picture ISIS returning to Syria in the next year or so. Heck, they did the same thing in Iraq. Every time the Iraqis thought they had ISIL beaten, they’d come back around again.
Things will improve but many parts of Syria (including parts of Damascus and its suburbs) will never be totally safe as was the case before the war. There will be some kind of low intensity conflict existing there for quite some time. No amount of Russian money and weapons can totally suppress it.
“I can easily picture ISIS returning to Syria in the next year or so.”
Many tribes in Saudi Arabia extend across the borders into neighboring countries. The Wahabbi-indoctrinated Sunni tribes around Euphrates River Valley in Syria and Iraq formed the heartland of ISIS, and its core cadre. Many (most) of those same tribal leaders still hold their positions.
One significant new aspect of the likely next peace settlement, could be Kurdish security forces (SDF) operating in traditionally Sunni areas along the Euphrates (Deir ez Zour Province, Raqqa/Tabqa). The Kurds have a world-class reputation for effective internal security against terrorism, and human intelligence gathering. Having them run the area could be the best long term solution toward managing those populations, to prevent re-emergence of ISIS-like groups there.
“There will be some kind of low intensity conflict existing there for quite some time.”
Although I (we) agree with gandalftb that the Syrian conflict is approaching a new more stable phase, that could be called “end of the war”, this is still the Middle East, and the many players will continue to scheme against, and back stab each other.
I think it likely that external patrons of many of the Sunni jihadi groups (US under Obama, Saudis, Gulf Arabs, Jordan) will agree to stand down the armed struggle and reconcile with the Syrian Government, even if Assad remains. Erdogan in Turkey however, seems to go his own radical way, and remains a wild card.
The fate of the Iranians is the biggest wild card in any upcoming stabilization. It will be very hard to get them effectively out of Syria, without regime change in Iran itself. They are very sophisticated with covert efforts.
A big change is brewing in Iraq now, after Muqtada Sadr’s list came out on top in the recent elections. His boys (Shi’ites yes, but Iraqi Nationalists, and with independent financial interests) are rooting out their competing Iranian-backed groups from a whole bunch of Government offices and lucrative rackets throughout the Shi’ite South of the country. Mobs are in the streets and blood is being spilt. It is a significant loss of Iranian influence, but they (Iranians) seem to be maintaining their footholds in Diyala Province (between Baghdad and the Iranian border), and the PUK Kurdish areas around Sulaymaniyah for now.