Speaking to the original question, strictly speaking, No, you don't have to bottle or keg. Your could cask your beer as a traditional Ale would have been.
Yes, it is perfectly safe to taste your beer at any stage of the brewing process. Just before bottling, your homebrew has already gone through every change necessary to turn it into beer and you will simply be tasting warm, flat beer. You get to taste beer!
Quick answer: probably a lot longer than you'll be able to keep yourself from drinking it all. Long answer: If dispensing with CO2, and maintained at the proper temperature (35-43 °F) and pressure (10-15 psi), homebrew will remain fresh for at least 6 months.