A.P.
I can see your dilemma. I would be torn as well. Here are the advice I have regarding some of the questions you have asked. First of all regarding the breast feeding, your milk supply most likely will go down if you pump and it may be more of a hassle to pump than to bring your son along and just nurse him. For example whenever you pump you most likely will have to be in a private place and that will limit being able to go out and do things whereas with your son just bring a blanket along!And even if you pump as often as you feed your son (which will most likely be hard when you just want to have a good time) your milk supply will probably go down because pumping does not maintain your milk supply as well as nursing at least a couple times a day does. Now you could consider weaning him since he is almost a year old. And are you going to pump and store enough milk for the whole time you are gone? That is probably going to be a lot of work for you. And if not, then he will have to have some formula and it is possible that he may end up weaning himself (which is not necessarily bad but it is up to you). Also, as far as him not sleeping through the night that would stress me out more to know that my child was keeping someone else up at night but maybe your mother-in-law doesn't mind.
Is there any way to push the trip back several months to when he is a little bit older and then you can go later with just your husband? In one way, it could be a really fun family vacation but on the other hand it could be a nice romantic getaway. When babies are over a year old it is easier to leave them because they are no longer nursing and Should definetely be sleeping through the night by then and they are more independent. I do not think that you will damage your relationship with your son by leaving for a vacation but it could be hard on you. It is still hard for me to leave my daughter for a few hours and she is 14 months. Anyway, good luck deciding. Hope this was more helpful than confusing! Oh and also I think he will be fine on the plane. Our daughter has been on planes several times and she does fine