Like any other quality game GOW would certainly help Vita. But for me GOW isn't a game for which I would buy a system. From a perspective of a Vita owner, I don't think that Vita needs to be "saved". Do i wish it would sell better? Sure, who doesn't. But that can only be achieved with significant price cut and continuous software support. 

I would rather see Heavenly Sword on Vita. At least Nariko is a likeable protagonist. 

Not by itself. It needs a steady stream of high-quality games. 1 or 2 good games a year won't do it. This is business 101 for making a console successful.

By alone it wouldn't save the Vita, but it would be one damn good direction to go towards that goal

Because it's a very popular franchise that performs well in general, but also on the PSP. Vita needs multiple games of that stature, among other things (e.g. price drop) to save itself.

I think I need "saved" defined because if a new God of War was released on Vita in a vacuum I would expect it would sell well and cause a little bump at its release. If followed up with little else it would likely fade away and be ported to PS4 as downloadable title. I don't think it is fair to put such a burden on any game on any system though.

It isn't one game that saves a system. It is a library of games. Look at the ps3. It doesn't have any truly popular games. It has large quantities of niche games that no one has ever heard of. Games not a game save a system.

Well, it was among the best games on the PSP, and it had strong sales. I think that's mostly why people could see it help. I also think it will, but not nearly enough to make it a competitor.

No. it would be great game to add to the library. Vita doesnt need any more spin-offs, It needs a title of its own that you can only find on the Vita, something that makes the system feel unique.

Well God of War has a bigger fanbase than all of Sony's other IPs by light-years, over 4.3 million fans on the FB fan page which is more than double the 2nd biggest Sony IP, so if they create a great quality exclusive God of War game for the Vita it will entice millions of GoW fans to buy a Vita which will help a lot, probably more so than Gran Tursimo would since that franchise isn't nearly as beloved or popular as GoW, without mass bundling I doubt it'd be much bigger. Although as some people have said, one game alone won't make a big enough impact no matter how good it may be.

Aside from a GoW game or to a lesser extent a fully featured GT game, what the Vita really needs is an exclusive (even temporarily) Grand Theft Auto game and something that'll be popular in Japan. If they release all these games and they are of a high standard then the Vita could start doing very well, first it needs a price cut though.