This is not an ailment with a cure. Unless medical science goes from knowing precious little about autoimmune diseases (and even less about their causes) all the way to knowing how to cure them, Venus will have to deal with this for the rest of her life. The goal with these ailments at this point in time is simply managing the symptoms as well as possible.
Venus is lucky in one respect: most autoimmune diseases don't even have names yet. They are among the least well understood problems of the human body. At least her problem is one that has been identified, so they know a little bit about it.
Her continuing to play tennis competitively certainly is in doubt at this point. Thank God Venus has a life and business interests outside of tennis. Still, it's clear she loves the game and wants very much to continue to compete, so I feel sure she'll try -- which may end up being an increasing source of frustration for her.