The last mining node probably stopped mining because of the mining-diversity rules in the chain, which place a limit on how many blocks can be mined by a single node.
But what do you mean by "putting genesis back into the chain"? The way to recover from this situation would be to bring up another of the mining nodes with -reindex=-1 but it is crucial not to overwrite the wallet files, because these contain the keys that give the node mining permission. Are your IP addresses also the same? If not you'll need to call addnode to help the nodes find each other.