I don't think US,France will ever leave Syria... and for the following reasons...
1)They have nothing to lose ,and too many things to win...
Nobody cares in US about US illegal war there as long no consequences for Americans troops.
The same is for france.
2) Syria is the world best place , in an unique time in history ,that NATO have to spy and analyze
Russian weapons. For example the Pentagon will have never know about Russia Electronic warfare
powerful capabilities.. had it wasn't for Ukraine and Syria conflicts that they created... So NATO
can now develop a weapon..a new missile ,a new electronic warfare technology . use it in Syria
and test it against Russia air defenses.. or Russia airforce. or Russia communications. To see if they
can jam Russia communications. NATO also have an unique opportunity to learn how to counter S-400s
and S-300s that is the backbone of RUssia air defenses.. So expect to see in the near future ballistic
missiles used... using conventional weapons.. to force Russia use their S-400s.. So NATO can learn
invaluable information about Russia military and its tactics.. for totally redesign their military tactics
and create new technology to counter Russia military capabilities.
3) No negative consequences for them... they don't lose soldiers and pilots and even have a deconfliction line
with Russia.. So is like a deal.. NATO don't overthrow Assad and in chance Russia teach NATO how to improve
their offensive capabilities against Russia.
4) US and France also before leaving , is important that they create strong propaganda ,that makes them look like they were truly fighting terrorism in Syria contrary to what Russia Military was saying for long.. of US UK and France
alliance with ISIS and Alqaeda in Syria.. So major PR propaganda will be done with NATO "Defeating ISIS" and other terrorist ,so to create a smoke screen , that confuse people about whether or not Russia claims of NATO alliance with terrorist was true or not.
When i say never.. it means never.. Regardless of who is in power in Syria .. NATO have an invaluable place in
the world ,where they can test their weapons .. This could save them a ton of of money.. if for example they find any
of their cruise missiles are useless..against Russia air defenses, then they will know they can't manufacture more of them..and will have to go to the drawing board again..and produce something else..
At the same time ,Russia also learns from NATO... so both benefits from learning how to better fight the other.
In the short term ,this will benefits more Russia than NATO.. since NATO is mostly used outdated missiles ..But once
NATO start producing Fast missiles then everything will change.. Don't be surprised if NATO use ballistic missiles
with multi entry conventional warheads. to try to test S-400s capabilities.
SO expect more chemical weapons BULLSHIT accusations/or barrel bombs in hospitals, against Syria ,that NATO will claim Assad did in order to justify more attacks.. and so they test their weapons.What Russia needs to do .to stop this dangerous games... is gradually incite Kurd rebellion ,a free kurds army.. that fight against Kurdish authorities and against NATO presence in Syria.. and start major armed insurgency attacks on US,france bases illegally there in Syria.
If Russia just stay there in Syria , defensively only.. taking hits from NATO
and not fighting back in some way ,directly or indirectly ,so to make it very expensive their illegal adventures in Syria
then Russia will only be encouraging NATO to never leave Syria and also help NATO to understand Russia military
capabilities and limits.
So Russia will need to start preparing to respond NATO with their own tactics.. using proxy warfare ,and provide
weapons to kurds friendly to Russia.. to defend their sovereignty and push NATO away from Syria.. also this can be combined with major peaceful anti NATO protest.. so the world see.. and increase the public opinion pressure against US and France to abandon Syria.