Perfectly good choice
If the party affects your son's care in a detrimental way, of course you would choose your son over the party.
But now I'm trying to understand how this affect would happen.
Hmm.
Loss of father over a 2 day period.
Something tells me it won't hurt him emotionally or physically, but for all I know you've been the primary care giver, have taken him with you to work every day, and he is so superadvanced (he is YOUR son, ya know) that he's reached the development stage where separation anxiety is an issue.
Party in early July, SETI born in late November, SETI will be about 6.5 months old. Since self-awareness usually kicks in between 8-11 months, I guess it is possible.
What else?
Lack of trust of non-parent caregivers? After all, your wife is a very busy person, which means you guy juggle the care time. If you have no fall-back for someone else doing it, could be an issue. I know I trusted NO ONE with my kids other than Barb and myself for the longest time.
Cost - you make so little that the cost of the trip will cause a balancing act to fail, robbing your child of his food, shelter, and finally his college fund. Hey, if that's the case, I'm sure we could kick in for airfare. ;-}
Lack of stability of spousal unit. Since you never said a bad word about a crazy wife, I doubt that is it.
OK, I don't see it. Maybe there is some indirect aspect of SETI's care that the party will affect.