I think it is normal to have some worries. If you are really concerned about something, could you consider counselling with your fiance?
As for having his Dad at your wedding - please mention him. It is important. When one of my nieces got married, it was a beautiful and happy day and it was made even more special when her sister (who had passed away several years before) was mentioned. We all cried, of course, because it is sad that she wasn't there and we all miss her so much. But it was good to go through it together.
Just thought of this - if there is a poem or something that your fiance's Dad liked that would fit into the ceremony, why not have someone recite it? Or something like that, to make him more present.
I wish you both the very best on your special day.