There are federal laws on how to fire people. It’s illegal to fire him for the reason that he’s prosecuting the presidents friend. If he can swing it he should immediately get a lawyer and challenge this. He will definitely win and get back pay but would he want to swim in these tainted waters?
I feel like this is the whole point of the regime’s lawless actions. Firstly it will take time for their action to be overturned in court (if they even comply) and secondly the person / organization reinstated that way probably won’t stick around long after. Either way is the same result to them.