I predict it will have a miserable, drawn-out, and dwindling end kind of like Vietnam.

Successful "Afghanistanization" (meaning defeat) will be cynically declared at some point as if it was a victory, and the Allied coalition will crawl off miserably back where they came from, pretending that the place is better off for them having been there. Fighting will continue between rival Afghan factions for awhile after. Then somebody else will assume power in Kabul and things will sort of slowly fester back to relatively "normal". Maybe. That's the most optimistic view, anyway.