Starfleet assumed that it was just a seismic anomaly. You;d think that if there was a ship capable of getting off the planet the Enterprise wouldn't have been surprised when they arrived. Seeing as Nero has had his ship rammed once already by a less advanced vessel you'd imagine he's not too keen on letting anyone get into a position to do the same.
Easier to imagine that any ship attempting to take off was destroyed. The Romulans managed to take out the rest of the fleet in just a matter of minutes. The Enterprise wasn't that far behind them. Wiping out some civilian ships would hardly even take a fraction of their weapon capability.
Depends on the number...
I can't see Nero wanting to waste the resources to hunt down hundreds or, more likely, thousands of craft fleeing Vulcan. Plus, you'd have to imagine that many craft would be taking off in the sensor shadow provided by the planet.
Ten thousand surviving Vulcans seems incredibly low for a race that likely numbers in the billions and has had space travel for a couple of millennium.