I've done my share of solo diving while diving with an insta-buddy, so the bottom line is to make sure you are prepared for a solo dive even if you aren't diving by yourself! I carry a 40cf pony on most dives, so if I get bailed on, I have a back up!
I did a solo dive on the Adolphus Busch last year. I was paired up with a guy who wanted to take pictures (Italian guy who spoke broken English, but enough to get by) Since there was a little current, we were told to jump in, and pair up at the mooring ball before descending. I jumped in, went to the ball, he jumped in, and reached up for his camera (nice rig with serious flashes and a huge dome port etc.) and started fiddling with it, not holding on to the rope. He started floating away around the side of the boat. The DM looked down at me and said "are there still bubbles on the line?" I looked, and saw some so I said "yeah" He said "go follow someone, I'm pulling this one out!" So I went down the line (past a lady who had the FEAR OF GOD in her eyes, and a very pi$$ed off looking husband) and paired up with a threesome of divers, who had no idea I was really following them. After the dive was over, I waited for them to take their first safety stop, then joined them on the line on the way back up. While we were waiting to climb the ladder, the one guy looked at me and said "where's your buddy" I said he never made it down, so I sort of followed you guys! He laughed and said "you were better off without him, he didn't look to swift to begin with!" So I dove with him, his wife and daughter the next two dives!