They're not being retired yet. The USAF have been trying to retire them since the day the Army forced them to get the plane in the first place, but the politicians stopped it this time like they always have done. But eventually they will be replaced by F-35s.
Yes, it will be replaced by the F35 - due to lack of alternatives. The F35 program has sucked up all available resources and that is part of the reason that a new CAS plane is not currently under development. A large chunk of CAS is going to be taken over by drones, but I do not think it is wise to rely on them 100%. F35 will fill up that role when needed, but not because it is good for it - because it is the only option that was made available.
