Sorry you are still dealing with the discomfort
to answer your athletic question, YES, you can still train and compete at those levels
It may take some time to figure out your body, since we have hydration issues.
I recently met a runner who is at the international competition level and he still competes. Personally, I have NEVER been athletic but I did train and finish a half marathon...and continue running because I LOVE IT. I know I have to be more careful because of my ileo but I know my quality of life is amazing because of it.
I think the key to everyone's decision is their quality of life. Yes, we have to make a difficult decision, but I think you said it best that you are living at 50-60%, and it's not something you sound comfortable with.
If you want to start with another loop ileo...do that. There is no medical reason you cannot. I would also see if you are a candidate for a j-pouch to cover all the 'what if' bases.