I suspect that the "security environment" in post-Soviet Afghanistan would have forced a military mission on the US fairly early-on. As I said, the US public would probably not have supported such action.
It's the same problem we faced in post-Saddam Iraq. You only need several dozen motivated trouble-makers with a few infantry weapons & some explosives and they can keep a neighborhood in an uproar.
It might have been a problem. The biggest problem we’d have had, the one that I think is the excuse used to do nothing, is that we officially had nothing to do with the Mujahadeen and stepping in would have broken that official designation. We lead a weird double life in that one, everybody knew we were involved, members of the American press even went over and talked to rebels and telecast stuff where they pretty much admitted where the weapons were coming from; but OFFICIALLY none of that was the case, officially we had nothing to do with it and didn’t know what any of these reporters were talking about. It was one of the most open secrets in US history.
It’s very possible the American people might not have supported it, much like many don’t support doing that in Afghanistan and Iraq now. It also very well might have failed. All these possibilities are there, the one thing I know for certain though is that I’d be much more impressed with our Cold War victory if we’d at least have tried.