"Remembrance" establishes that it was the Romulan sun itself that went supernova, with no mention of Hobus, or a chain reaction, or it expanding faster-than-light as the original Countdown comic or Star Trek Online: The Needs of the Many previously established. Picard left the Enterprise to head up a rescue mission that would save 900,000 Romulans but it all fell apart after the Synths destroy Mars.
So Spock's "a star will explode, and threaten to destroy the galaxy!" from Star Trek (2009) is rendered nonsensical, but "Rememberance" does explain why Spock went it alone, because the Federation withdrew support for the evacuation effort after the Synths destroy Mars. His was a last ditch effort. Nero's cries that "The Federation did nothing!" are confirmed and his vendetta against Spock is about him breaking his promise to save Romulus - although Romulus could never survive without a star anyway so...
So Spock's "a star will explode, and threaten to destroy the galaxy!" from Star Trek (2009) is rendered nonsensical, but "Rememberance" does explain why Spock went it alone, because the Federation withdrew support for the evacuation effort after the Synths destroy Mars. His was a last ditch effort. Nero's cries that "The Federation did nothing!" are confirmed and his vendetta against Spock is about him breaking his promise to save Romulus - although Romulus could never survive without a star anyway so...
