Oh my gosh, this is something close to me as I JUST went through this!
Anyway, seven years ago I backed out of my best friends wedding. I did it along with another friend and we did it over the phone. In hindsight, I know it was the IMMATURE way to handle it and I have always regretted it deep inside. Obviously, there is a lot more to the story, but we stopped talking.
I still heard about her through other friends and her first daughter was due within days of my first son (they will be three in June). We both struggled with pregnancy for different reasons. So when I heard she was pregnant and due at the same time, I dropped her an email wishing her the best. I made it clear that I wasn't trying to rekindle a friendship - only that I wished her the best with her pregnancy. She wrote me back, thanked me for the well wishes and offered the same to us. Done deal.
This past year, she had her second daughter and I delivered our second son. After months of thinking about it, I wrote her an email at the end of January - not apologizing - but just telling her that I thought of her often and hoped that she has found as much joy in her girls as I have in my boys.
She wrote back and suggested meeting. After a TON of emails, we couldn't wait to get together and had a 3+ hour lunch. It was like very little time had passed - not seven years. I was SO happy that I contacted her and I was able to come to terms with how I had hurt her so long ago. I didn't apologize for my decision to back out of the wedding, but for my immature way of handling it. I can't change how I handled the situation, but we seem to have gotten past it.
I don't know where it will go from here and how close we will ever be. But, I'm open to whatever she (and her husband) are comfortable with.
So, if you ask me - I say go for it. Lol.
EDITED TO ADD: I agree with Kate's post - don't expect too much from it. I sent my email just to let her know that I still thought about her and wished her the best. I really had no intentions of anything coming of it. I was SHOCKED when she wrote back - the same day - and said her first thought was to get together. She very easily could have said, "What you did was unforgivable please leave me alone." I knew that was a possibility when I decided to write (which is part of the reason I didn't tell anyone I was doing it!).