Here's what you should do.

1. Based on prior experience, expect nothing from him as a grandfather or in his will. If you get more that that, consider it a bonus.
2. Distance somewhat from him because his current situation is rather gross, I agree.
3. Don't predict whether this specialty fertility procedure will result in a baby, or what it's life will be like if it does succeed.
4. Don't predict if a baby does result, that he will only be in that child's life a short time. He's 58, he could live another 40 years.

What I have recommended requires you to be a little zen, but if you can achieve it, your upset feelings will be minimized. Good luck with your own family and baby plans. That is where you should focus your attention.