Far from expert 2 cents
Iran's issues with the Taliban were a MAJOR missed opportunity for the US to bag Al-Qaeda with the Iranians doing the heavy lifting. Unfortunately, given the extensive Saudi-financed ISI mucking about, it would be unlikely for the Iranian-banked NA to prevail as they did with US support in 2002.
Badass punitive expedition that topples the Taliban as ruling government or weakens them to rump state needing extensive Pakistani support is likely though. The NA ruling the area effectively is a whole different matter.
I figure Afghanistan'd end up with a buffer zone 40% under Iranian control, a buffer zone of 40% under NA control, 20% under quasi-Pakistani control, Kabul being a free city, lots of UN sanctions on all involved with a massive refugee crisis and maybe some blue helmets policing the buffer zone a la Cyprus.
Chances of it being a "failed state" like Somalia, 95%, solving one problem but causing a ton of problems later on for various neighbors. IDK what tensions exist between Iran and Pakistan lately-- but spanking ISI clients
would bring a nasty cold war forcing both Iran and Pakistan to spend a lot of time and money snarling and tussling with each other with OOTW. (Ops Other Than War for Austin Bay fans). Iran and India cooperate a lot anyway, but they'd likely be in a much tighter military and economic alliance if this op goes down.
If the Iranians and US could come to some kind of cooperative agreement, this could work wonders for their ongoing relationship, but too many in the US didn't want to cut their ISI "allies" loose, had grudges from 1979, etc,
and Iran had severe trust issues the US'd hold up their end.
Anyhow, just thought I'd toss in my bits.