First of course this is not recommended, since it wouldn't make a great deal of logical sense.
But essentially each node would behave in accordance with its local policy. So each node independently decides, based on its mineemptyrounds runtime parameter, whether it is valid to keep buliding blocks on the chain or not. Those that think so will do so, if they are permitted to build the next block. Those that don't think so, won't.
What happens in practice, in terms of whether blocks keep getting built in the long term, will dependent on the combination of these runtime parameters and the mining-diversity blockchain parameter.