I'd don't know what the percentage is, but I'd have to guess its as high as 75% of scuba deaths, the dive buddy is no where around. Live longer, never leave your dive buddy.
How many people who insta-buddy dive take 60 seconds before splashing in to actually discuss sticking close to each other, discuss hand signals, and then how many during the dive at least once ask for their insta-buddy's air pressure during the dive and give theirs? I don't see it happening.
I was on a dive on this very dive site last year, when there were 2 divers on our boat without buddies, they both splashed in without even buddying up together, each one penetrated the wreck solo, just hanging around the vicinity of the group of us 3 pairs of buddy team divers, not close to each other, sometimes one would be at the head of the group and one buried 4 divers back in the single file chain snaking through the wreck.
One of the solo divers went OOA on his safety stop and his personal lesson from it all was that he couldn't trust a rental gauge that said he still had 300psi on his stop, he felt that if he had a reliable accurate gauge he would have been fine.
I really wish people would take the dangers of scuba diving more seriously. I've seen too many husband/boyfriends downplaying the seriousness of the dangers of diving to their wife/girlfriend-vacation dive buddy out of fear of them becoming too nervous or not wanting to risk them not wanting to dive.