The times I have been without my buddy on a trip and assigned an insta-buddy, I follow the Chairman's rule.
I've never had a boat chew me out for popping a sausage. I've shared this before, but it bears repeating.
A friend and I were diving a charter I had never been on before in the panhandle of Florida. He set the dive up, so I know no one. I tried to make myself known as much as possible to the crew, even mentioning that I am the owner of SB and all. We do this deepish reef @ 80fsw and we go down their anchor line which was 15 ft off of the reef and there was a dead nurse shark. We swim to one end of the reef, double back and swim to the other end of the reef. Deco is at hand, so we find the shark and go to start up the anchor line... only no anchor. We make a bigger circle, still no anchor. We're into deco a couple of minutes, so we decide to go ahead and head up sans anchor line. At 60 fsw, I shoot the bag. We surface and, of course, everyone else is on the boat. The crew makes some comments about staying below too long, and we set about to change our tanks over.
Then one of the other divers comes over and tells me what I didn't know. They were steaming off when my bag hit the surface. In fact, he was the one who happened to see it break surface and asked the crew if they had left anyone. They had done a roll call, but someone suggested that my friend and I were on the bow. Moral? If you think you're lost, you are. If something is weird, you're lost. If you can't identify exactly where you're at, then you're lost. Don't deny it. Shoot the bag. Shoot the bag NOW. Don't wait for a safety stop. Don't pass "Go": shoot it now, now, now. You'll be glad you did! We'll be glad you did!