We left our son for about a week while we went to NYC -- when he was 2 yrs old. He never fussed or cried for mommy -- I really don't think he realized we were gone that long. Children at that age don't have a good concept of time. It was good to call in - at the most, once a day - to see how things were going or to see if my Mom had a question. But everything went great and it was good to see my son bonding with his Memaw!
And you and your husband need time to bond alone, too! This is crucial for your marriage --- and ultimately builds a stronger foundation for your family. A parent's greatest gift to their child is a good example of a good, healthy marriage. We try to get away twice a year -- even if we're short on funds -- we'll at least go to a bed-and-breakfast just outside of the metroplex for a long weekend -- so nice to have that -- to remember that we are a husband and wife first and then mommy/daddy second.
Also: I would recommend nixing the sleeping with the kids thing. Your kids need to build self-confidence and independence -- and that starts in small doses - like sleeping in their own beds....plus, it'll help in the transition when you guys go on your trip. Plus, do you guys have any alone, wife-husband intimate time that way?? Plus, it'll also be good for you to wean yourself off so you won't be in shock when you're not sleeping with them on your trip ... you'll be able to better relax and enjoy the trip, if you've already establish a routine of not sleeping with the kids.
Like another comment posting, I would also start leaving the kiddos in small doses with the grandparents or other family members so they get used to that idea... one night here...two nights there. My son spends the night at least once a month with his cousins or his aunt/uncle or grandparents. So he never really has separation anxiety and loves the change in routine. It's a new adventure for him and he loves it.
Good luck planning your trip!
-A.