I'll never really understand what "save" means in this context. All I can think of is that it implies that the Vita will be discontinued, which isn't going to happen, so it's already saved.
Therefore, I'm going to approach this as if the question were, "what can help the Vita perform better?"
Many things would fit that criteria, to differing degrees. In Japan, it's on the right course. Sony stopped assuming developers would simply jump to support the Vita and started working closely with them instead. Several "partnership" games have been released with more on the way. Most of these will contribute to a soft rise in Vita sales.
I don't see anything that would automatically result in a sharp spike on the horizon, however. KanColle has the potential but it's going to depend on the game itself. Nothing is known yet. Monster Hunter would but, obviously, no announcements. I'm pretty sure the Vita will get a Monster Hunter game eventually, though, even if it's a couple of years away.
In Europe, I think the Vita will do okay. A Gran Turismo game would help a lot.
In North America, it would have to have more games aimed at children, of which we've seen no signs. This is probably Sony's biggest failing with the Vita. They should have had several kid-friendly IP ready to go from the start.
Some big western IP would help in general but it looks like the principle publishers over here have dropped Vita support before it's even begun. They're pouring all their resources into the XO and PS4. I think it's never going to do nice numbers in North America.
So, really, it will do moderately well in Japan, okay in Europe, and bad everywhere else. I don't see much to change that, honestly. Still, Japan was always going to be its best market. It can be a success based on that alone. With the alliances Sony has formed, and what has already been announced, I'm positive about the Vita going forward. It's going to get Japanese developed games, a few of which will have a nice impact.
On a personal level, I like Japanese handheld games, so I'm happy.
