I'd put father brain's scenario at a roughly 0% chance of happening. Even if they internally decide(d) to give up on the thing, they're not going to come out and say it. That kind of thing really only happens when you are permanently checking out of the market.
Are you saying that you expect Sony to try again with a third dedicated handheld platform, or just that you expect them to continue some token level of Vita support for another few years? The latter could happen, but I don't see how the former is at all plausible.
I'm not expecting it would be announced in a particularly conspicuous way, i.e. getting its own press release. Just a sentence or so in one of their future earnings releases, or being absent from their FY2014 forecast.
...also, forecasting only 3-3.5M shipped this FY is already
almost as close as they could get to giving up without officially giving up. I guess the forecast could have been even lower, though?