Last I read we WERE keeping it (until 2021 anyway). I think anybody will be 'hard-pressed' to come up with a better design and/or cost effective replacement. I see it being the B-52 of CAS meaning it will be here for a LONG time.
FB-111A Pease AFB 82-87
A-10A Suwon AB ROK 87-88
FB-111A/F-111G Pease AFB 88-90
If we were to get into a serious war with Russia or China in the next few decades, we'd soon decide that we needed more planes for hitting targets on the ground. It doesn't even matter which type (Thunderbolt/Falcon/Lightning) we have the most of at that point; it will just be a matter of not having a large enough number of them. The solution will be to pick one type or another to order a lot more of on short notice. And that will result in a new production run of brand-new Thunderbolts just because it's quicker & cheaper than the other basic options.
Hard to say. The A-10 is basically a sitting duck for a fully modernized AD network. On the other hand, the combination of forward deployment, huge payload, and long endurance make it the ideal CAS platform in uncontested airspace.