My .02Cr...
First, we should classify this as an unprecedented stellar event that created what could only be described as a subspace explosion. To go with a pseudo-scientific result, I'd say this "subspace supernova" (for lack of a better term) consumed all the interstellar medium in its path, and also any larger bodies, like Romulus and (likely) the rest of the Romulan System. Given that, to even threaten Romulus, the event had to be a faster-than-light event, it would almost-certainly create short or long-term navigational effects in that region of space. (Let's assume Hobus was 6-12 ly from Romulus, somewhere within the boundaries of the star empire. This would mean the explosion was traveling at a velocity of approximately wf9-9.25 (MCU).)
Second, the Romulans probably only had 2-3 days' notice at best, given that the Vulcan's "fastest ship" was likely close to Voyager's wf9.982 (MCU) top speed (I estimated it at 7000c). At that speed, the Jellyfish would take a little over three days to reach Romulus (60ly away, according to Star Charts). Complicate this with the fact that the stellar event itself was unprecedented; the Romulans may not have immediately realized that the Hobus subspace supernova was a threat to their star system.
Using a 6ly radius blast from within the RSE (that doesn't threaten Federation outposts before the destruction of Romulus), Star Charts inhabited planets Menkent, Terix, Belak and Algorab would also have perished. Nearby systems Romii, T'Met, Gacrux and Archenar would have survived.
The result is that most Romulans living in the Romulan system perished before they could evacuate, as well as any Romulans living on colonies within the path of the event. I would expect that the Romulan military and civilian leadership survived (they, at least, would be evacuated), though the total number of surviving Romulans likely number in the millions (or less, considering their penchant for isolationism).
So, what we have is a relatively new Praetor (less than nine years in office) having to move his seat of government to Romii (the closest surviving Romulan system). He was likely still in consolidating his power base, still dealing with enemies and forming lasting (well, in a relative sense) alliances. Some of the problems would have been eliminated, others exacerbated. Regardless, his grip on power is likely more tenuous...unless he acts decisively.
The Praetor broadcasts an impassioned speech, dedicating himself to rebuilding the glory of Romulus, calling on his fellow Romans to help him and warning the enemies of the empire that while it may be wounded, it is still a powerful force to be reckoned with (the RSN is likely still mostly intact). The star empire turns inward in a massive national project to turn Romii into the new center of Romulan culture. They attempt to defend their border against the Klingons, while continuing diplomatic overtures to the Federation (mostly in the hopes that the Federation will keep the Klingon dogs at bay).
If forced to fight, they will, but they would prefer to isolate themselves for a while to rebuild their strength.
However, I think that there will be more Neros out there than the Praetor desires...and some of them will be wearing a naval uniform...or, worse, a Tal Shiar uniform...those who have lost just about everything have nothing to lose, and with a battleship at their command, like along the Federation border will be "interesting" for a while...
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz