If he doesn't regret the estrangement now she's died, then it's unlikely he will regret not going to the funeral. However, attending it could provide 'closure'.
I do hope people aren't going to post how sorry they are for your loss.
Boycotting the funeral would be a bold statement, but haven't you already made that in the last 16 years? I would ask members of the family what they would think if you didn't attend.