We really have no idea what, exactly, happened after Romulus was annihilated and Spock saved the remainder of the universe. All that we know is that Nero's ship and the Jellyfish were close enough to be sucked into the new timeline.
I'm strongly inclined to think that Romulan civilization has survived the destruction of the homeworld (and, perhaps, even some of the older and closer colonies). The novels particularly have established that Romulan interstellar civilization is older than human interstellar civilization, that Romulus has numerous colonies and protectorates, and that at the time of the Romulan War the Romulan sphere of influence was substantially larger and more developed than a human sphere of influence that stretched as far as Deneva. There's less reason to think that Romulan civilization will be destroyed by the loss of Romulus than there is to think that if (say) the Borg supercube had destroyed Earth human civilization would become defunct.
While we know that the Romulan state is more than Romulus, there does seem to be a pretty strong psychological identification of the homeworld with the entire empire. I'm sure part of this is from the whole "ROMAN EMPIRE IN SPAAAACE" element, but the impact of losing the homeworld would, most likely be extremely traumatic for the Romulans in a way that say the secession of Andor wasn't for the Federation.
Part of the endurance of the Romulan state will depend one what exactly binds the empire together. In the novels it did not take much post Nemesis for the Empire to split into two political entities. The loss of Romulus and any other core worlds might be enough for it all to fall apart.
If the Empire is maintained with terror and fear, then the loss of the core of that fear would change the equation. remember, unlike the Federation, the bulk of Romulan space would have to be occupied by subject worlds (I've always had a problem with the idea that monocultural/ethnic empires could ever match the size and power of the multicultural Federation). Those subject worlds might take the opportunity to break free of the rump RSE….much as the occupied/subject states of the former Soviet Union/Warsaw Pact used Russia's growing weakness as an opportunity to break free.