I work on the A-10. The F-35 is supposed to replace the A-10 (at least most of it's roles), but it can't. It is simply in a different performance envelope. Not better or worse, but different and definitely worse for the 2 most important roles the A-10 plays: Close Air Support, and even more important, Combat Search and Rescue.
The F-35 is a boondoggle (go watch "The Pentagon Wars", and imagine the same thing with an airplane, and waaaayyyy more money). I work on Hill AFB, I see the F-35s flying over every day, and it's a cool plane. Fast, loud, (really loud) and a hangar queen that is almost as bad as the F-22!
Luckily, the A-10 is funded through 2032. Long live the Warthog!