If Vulcan is destroyed in the past and the timeline irrevocably changed then Picard and the Enterprise may never exist, which means they did not travel back in time to stop the Borg, which means earth was assimilated in the 21st century and nothing in these stupid movies has happened.
shareIf your a fan of all the tv shows as well, you would know that with no Picard and his crew in the timeline the Borg would not have needed to travel back in time to the 21st century. Earth would almost certainly have been assimilated by the borg at some point with out The next gen crew to stop them but it would not have happened until the 24th century. This means that the borg have pretty much zero effect at this stage on this new timeline.
2 words:
Alternate timeline.
Simple as that.
What didn't make sense where the bad guys. I mean how stupid are they? First they get angry at the guy who tried to help them. Then when they go to the past instead of trying to save their planet they go on unrelated mass murders?? How about doing something so Romulus won't be destroyed again???
shareNero seemed to be a stupid villain on all counts. If he went back in time, as has been mentioned, he could have warned Romulus and they could have evacuated the planet. He also has no reason whatsoever to blame Spock or the Vulcans in general. Vulcan is a Federation planet. The Federation are under no obligation at all to help the Romulans. The Romulans were willing to sit back and do nothing when the Federation was being attacked by the Dominion (who would have inevitably turned on the Romulans after defeating the Federation and Klingons. In fact several years earlier, Spock had tried to make peace between the Vulcans and Romulans, but he was betrayed...by Romulans!
sharethe Borg won't arrive in the alpha quadrant for a few hundred more years, and they won't be out there looking for the Enterprise which mysteriously flew at speed far greater than their technology should have allowed (thanks to Q). So if Q doesn't send the Enterprise out there, the Borg won't come looking for them, and the Earth won't be invaded. The butterfly effect, one change leads to another which leads to another, and so on.
"He's dusted, busted and disgusted, but he's ok"
You answered your own question.
"If...the timeline irrevocably changed then Picard and the Enterprise may never exist."
MAY never exist. Not DEFINITELY DIDN'T
We don't know how the timeline being changed in the 23rd century has affected the 24th yet. Picard and the Enterprise-D might exist. Or they might not. There are definitely things going on in the movie that don't make sense (like how the Enterprise was able to warp away from the newly formed black hole when they had just jettisoned their warp drive). But the postulation that the alternate timeline will cause Picard not to exist is not one of them. It COULD cause him not to exist. But while this may be brought up in future movies (I've not seen the other two yet, so I can't speak to them), there's nothing in this particular one that suggests that.