GO! Seriously, GO! Seven years and you've never been away from your kids with just your husband? You need this. Your husband needs this. And, believe it or not, your kids need this. This will be your first step of many in learning to let go (little by little) in order for your children to learn how to live to be responsible, independent, fully capable people. Considering what you've said, if the worst that happens is that one of your children wakes up asking for you, then it will a learning experience for that child. They will learn that they can be away from you and will be okay. They will learn that it's okay to miss you, but that you will come back. They will know that when they get invited to a slumber party, they can handle it...and so can you. They will learn that their parents love each other and that it's important for parents to have time together. They will learn that while they are the center of your lives, your world doesn't actually have to revolve around them - that you have lives and important needs of your own. They will learn that their needs can actually be taken care of by themselves sometimes. They will have fun, but will likely miss home and will learn how much they love the home you have made for them.
You will likely talk about your kids for the first few hours of being gone and it will be difficult to break the cycle and learn how to talk to your husband about something that doesn't relate to the kids, but do try to let go and just enjoy yourself and bask in the moments of it just being the two of you. This is a great opportunity to re-connect and a wonderful gift your friend is giving to both of you.
Definitely GO! :)