Re: What happened to Vash?
I don't think she's appeared in any of the novelverse stuff, but we did meet the MU version of her in the TNG MU novella, The Worst of Both Worlds. The other day the official Star Trek website posted a preview of Hive, the comic co-written by Brannon Braga, and it showed a Post-Nemesis Picard getting together with her.
Over the course of many encounters and many years, I have successfully developed a standard operating procedure for dealing with big, nasty monsters. Run away. Me and Monty Python.
Harry Dresden - Blood Rites (The Dresden Files #6)