Let's say he's recalled. Is there a new vote? Using the same machines? (!) Maybe a law change should be first, if so, banning corruptible, hackable machines.

Also, can the supervisors be impeached?

Impeachment at the State Level. At the state level, civil officers who can be impeached include judges, legislators, governors, and other officials throughout the ranks, generally mirroring the federal impeachment process. Several governors have been impeached and eight have been removed from office.

https://en.wikipedia.org/wiki/Recall_election#United_States