Meh, there are many worlds in the Empire, Romulus was but one. (That is, if there was any saving it: the supernova could have been a natural phenomenon or not of their doing.) And the breakdown into multiple Romulan fiefdoms might suit the Romulan families just fine in their inner clashes with one another. Similar to the Klingons of earlier centuries. We don’t know how united the Star-Empire actually was or what was going on inside. I mean, they disappeared for 50 years and came back looking very differently than before.
They could still be...and probably are playing their 4-D game of chess with the rest of the galaxy. I mean, the Klingons or the Breen or other powers haven’t taken over the regional empires. They’re maybe not as out of the astro-political game as we might think. With probably greater concentrated power and control on their fewer, traumatized, citizens, and less bulk to worry about.
And, again, with the synths now on the biologics’ side.
PS: let’s not forget these are Vulcanoids we’re talking about. If not for their turn to logic their volatile emotions would have completely destroyed them back on Vulcan. Some think Vulcan itself was a green world before they nuked themselves to near total annihilation and rebuilt on the ruins of their old world. Those that stayed adapted, those that left became the volatile Romulans we know. Here, further casting their death wishes into the void.