I agree with your assessment on all points, except that I think it might be possible for Turkey to annex some territory in a final settlement.
Despite that possible reservation, I think your assessment of no peace while Turkey remains is more likely, especially in Afrin. It would likely require an epic genocidal ethnic cleansing to enable Turkey to fully pacify Afrin.
Erdogan has chosen to do this ‘AS’ a NATO member.......this is the reason why NOBODY wanted Turkey directly involved when the push against ISIS first began. Everybody said No and Erdogan was beyond pee-oed......so here we are with this beast ‘invading’ in a war he was told clearly to stay out of.