I have a couple of friends who will break away and reintegrate. They are not welcomed back by everyone, but many people will reaccept them. With one friend who does this, we just pick up where we left off. It bothered me at first, but I understand why it happens, so I just accept it. It may be a shorter break than you describe, 1-3 years. Both of the people I am thinking of will be direct about the fact that they weren't feeling well. I don't think you have to be, but I also don't think people will get weird about it. Just about everyone has been depressed or knows someone who is depressed.

I have taken my own breaks and find that baby steps are the way to go for me. I am also trying out not getting too close to anyone too fast, since it's too easy for me to just form a friendship with the first person who asks since that seems easier than having to keep meeting people until I meet someone I really like. I definitely agree with what rcat said about acquaintances coming first.

In your shoes, I would probably focus on finding new friends and not expect too much from the college buddies. It doesn't hurt to try, but there is a huge difference between who you are friends with when you are 20 vs. 30 (in my experience). I guess what I am trying to say is that if your college buddies aren't that receptive to restarting the friendship, it may not have anything to do with you so much as it has to do with just being at a very different stage of life.