I don't know of any general rules for how long exposed film can be kept without deterioration - it will vary from film to film, as well as being temperature dependent. Tri-X and Kodachrome had good reputations for latent image stability, for example.

The first parts of the latent image to go will be the shadow details - the fewer silver atoms in the image centre, the shorter their survival time. I've noticed that the faster the film, the less stable the latent image shadow details are.

Re-freezing exposed film is no big deal, and I used to do it as a matter of routine when living in the tropics. Just wrap it closely (ie as little airspace as possible) in an airtight wrapper and put it in the fridge or freezer - the fridge is likely to be cold enough for all but very long delays before processing. Allow plenty of time for it to warm up again before opening the package.