Neal was probably the last person on OUAT who would want to see his family collapse because of his death. He told Emma to find Tallahassee – wouldn’t he want his father to move on as well? To me the wedding was a way to show that you can’t just shut down when you lose someone – they will always be a part of you but you must still live. Not survive but live. I t hink Neal would be happy knowing Rumple and Belle married because Rumple is doing exactly what Neal would want him to do.
And Rumple did attempt to avenge Neal’s death by killing Zelena (and in my opinion that is the LAST thing Neal would want.)