Here’s some things to consider:
This could be Russia’s last “safe” warm-water port and Assad going down means they lose it. I’d think they’d fight like hell for it,
If Assad goes down, Iran loses its last major ally in the ME (they can’t rely on the Houthis). As it stands, Iran can’t do a lot because its access through Lebanon is probably gone at this point, and it has to be wary of Israel when making large deliveries. Israel isn’t going to let Iran arm any groups around them, and they can’t go through the Kurds and Iraq, and definitely can’t go through Türkiye. .
Israel and Türkiye will happily let Assad fall and then watch the various groups fight each other. At some point they have to step in though and pick a winner (who will be stable).
The Kurds are nominally under US protection east of the Euphrates. If things fall apart, they could wind up breaking off in some form. Türkiye wouldn’t be happy, but they would help keep Syria divided and provide a buffer to Iran (not that Iran could move through Northern Iraq, but if they,,, somehow did, the Kurds would be waiting). There is the problem of Kurds in Türkiye and Iraq, but hell maybe the Turks would be happy with them leaving Türkiye in some manner and moving to what was Syria.
Speaking of Iraq, if things fall apart, the Western border areas of Iraq get dicey.
Crazy how this thing could spiral out of control so quickly and suck a bit of Iraq and possibly Lebanon into it. Also crazy at how much Iran and Russia really need Syria.