If you can't find the information on MSDN or MVP, then it's probably a good idea to ask Microsoft directly here (the C++ ones, I'd guess). I don't work for Microsoft but I do work for another (very) large organization and we developers monitor public fora very closely. I suspect there's quite a few MS developers who would be watching that site.
However, if you're doing project planning without risk management and contingencies, you're not doing it right.
You should allow for the possibility that it will not be supported and do one of two things.
- have an item in your Gantt chart to allow for the re-engineering.
- have a risk log that clearly states re-engineering may be necessary.
From my experience, the first is usually better since, if you find you don't have to do it and the schedule is slipping, you can just drop that item to catch up. Sometimes you can drop it anyway and deliver sooner, just to make yourself look better for your annual performance review :-)
But even if you don't allow for it and then find it's necessary, the risk morphs into an issue and you can go to higher management to explain why more time is needed. You're covered since it was made clear in the risk log - it then becomes their decision to allow you more time or keep using a back-level of MSVC.
Keep in mind that if you don't have to do it, you probably still should consider it (sans schedule slippage). Microsoft didn't deprecate them for a laugh, they're going to disappear at some point. Although YAGNI suggests you shouldn't worry about it unless it's imminent, it would be prudent to do some work on getting ready for it.
That will avoid the last-minute mad rush when Microsoft finally do remove the functionality.