Hi Athena,
I have thought about a similar situation within my own family.
First, don't count your uncle out so fast. He may not be in the best of health, but I have seen people in bad shape who survived and continued living for many years.
I agree that it doesn't hurt to have a plan should things go badly.
In my own situation, my parents are elderly and most of the family has nothing to do with me. I have openly hostile brothers, and one of them I am sure will officiate at a funeral. He has inserted himself in similar situations, like my mother's funeral, so I have no doubts about this. There is a strong possibility that I will not be invited to attend.
Several family reunions have been held where I was not invited and only learned of them several months later. When questioned about it, my father said that due to the animosity (pre-transition) between me and my brother, it was best if I didn't come so there would be no confrontations.
My dad's brother (my uncle) and one of his daughters have been very supportive of me. Although they disapprove of the situation, they would be an ally in any uncomfortable situation.
The thing to remember is that funerals are held for the living, not the dead. It is a chance to say goodbye and provide closure. I can do that without needing to see a body in a casket. And I would avoid any drama for me and others by not attending. I can always visit my uncle and cousin and spend time with allies during their grieving period.
I think what you need to consider is how close were you to the deceased, and whether will you feel an obligation to say goodbye and pay respects in person. If your only reason for going is to support a family member, you can do that by spending time with them before and after the funeral. That would prevent turmoil at the funeral itself. Sure, there will be some to criticize us for not attending, but in my case, there will be even more that are thankful if I don't.
I hope this gives you some things to think about and is helpful somehow.