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.

Best,
Helen