No, what would have happened is the lieutenant governor would have become acting governor, and actual governor if the previous governor were killed. Meanwhile, there would have been an insane level of manhunt. The perpetrators would have eventually been located, jailed for most or all of the rest of their lives, and, if the governor would have died, perhaps executed.

None of that would have come anywhere close to "overthrowing the government of Michigan". It might have removed the existing governor, but that's all.

I imagine the feds would have stepped in with the military to put an end to the ‘rebellion’.

Reading this story, my fear is that, if successful, Trump would not have been able to help himself from making statements that would embolden other such groups in other states.