Added:
Ok - just reading your response where you said "Just go and get it over with" changes my response.
If you're just doing this out of obligation or whatever - then I'd rethink it. I guess it would really depend on why you booked this in the first place .
Original: Why did you make the plans in the first place? It's because you wanted to see them.
So - given that, cancelling now because you feel you will miss your husband and son, is a wee bit irrational. Of course we miss people when we're away, but it's one week. I used to travel for weeks straight at a time when I worked and left my young family and husband home. You can do it - trust me. They will be fine, and time apart goes quickly (super quick).
When I have traveled (recently I saw my extended family) my kids didn't even notice I was gone. Instead of being disappointed (not saying you would be, but I kind of thought they'd notice I wasn't there) I was relieved. I have raised somewhat resilient kids. I think that's important. My husband also feels strongly I need to do things on my own - to replenish my soul to speak - so that as a woman, and of course mom/wife, I have my own things/experiences to contribute. Do it for yourself. I'm sure your husband would agree.
As for keeping it for savings, etc. Well - I just lost a family member. You never get that time back. I am happy I made the time along the way to visit. I don't think that should be your ultimate reason - but family is family - if you care about them, and they add a positive element to your life (your interactions with them) then by all means fit them in. And yes, they would be disappointed if you cancelled.
Is there some underlying issue here - perhaps anxiety or something that's nibbling away at you? I get that a bit at times. I would just realize it will all be ok - more than ok, it will be fun and a great opportunity for your husband and son to bond without mom there :)