Last I checked BIP110 will have a mandatory signaling window in August, so if miners don’t signal, BIP110 nodes will in fact fork themselves off the network. Your scenario could still happen if miners do signal (which non-BIP110 won’t care about one way or the other). That’s why IMO it’s still good to pay attention to signaling, and if there is any it’s probably time to start considering a URSF. The worst case scenario is if miners don’t signal until very shortly before the mandatory signaling period starts. (Or even when it’s already started.) In that case I suppose the rejectblock command can still offer a solution, but it’d be a bit of a last-minute scramble…