This can simply not be true. I have played with and without the widescreen mod and in several different resolutions without any problems.
Believe what you will. The facts are that the assets in Baldur's Gate are fixed aspect, and the widescreen mod has to physically alter them. The facts are that those altered assets are stored in your saved games. The facts are that if you load a saved game with altered assets into a game in another resolution, it WILL crash. Do your homework.
Well, I do not have to believe, I speak from experience, do you? If it is as you say then it is very strange that it hasn't crashed for me. I have played thru whole BG1 and half BG2 and moved save files between several different computers (5 computers to be exact) with different resolutions, with and without widescreen mod, and not experienced one single crash so far. So, how do you explain that?
And btw, do not tell me to do my homework, that is just plain rude, I just state what I have experienced, and I do not experience any crash in the scenario where you say that the game "WILL crash". I actually have 2 different installations right here at this computer I sit at right now, one with widescreen mod and resolution 1280*720 and one without widescreen mod and resolution 800*600, and I have over 100 save files, I have saved several of them in the first installation (with widescreen mod) and opened them in the second installation, and believe it or not, but no crashes. So when I do my homework it is very clear that the thing you are saying can just simply not be true. Maybe time for you do do yours?
Can it be that you have tried an old version of widescreen mod with bugs?