Good questions. I don't think people will like my answers, but..
* What would you do if you lost sight of your buddy underwater and couldn't find him/her?
Look around for them for a few minutes while using my DiveAlert (quack quack!) and then surface if I can't find them in time.
* What would you do if you're in a buddy team of 3 divers and one buddy went left while the other went right?
Quack, quack. It's going to get their attentions, and then I can signal to them that they're not making good decisions.
* What would you do if you're in a buddy team of 5 divers and, all of a sudden, you only counted 3 other divers in your field of view?
Swim up to someone and explain the situation, if they don't know, I'll ask the other two. The other two could have been air hogs and went to surface.
* What would you do if you're diving in two buddy pairs and you lost sight of the other buddy pair?
Depends on the dive, probably nothing, but that's just how we dive here. If our group has the dive flag, well then it's the other group's fault. If they had the flag...crap, time to deploy DSMB. The boat I dive on, people often break off and go do their own thing, especially when hunting. No big deal.
* What would you do if you got a leg cramp but your buddy didn't notice and left you behind?
Quack, quack
. Unless I can reach my buddy, or get their attention another way.
Also part of it is that there's always a DM in the water, and usually two. Not my job to babysit, but if I seem something odd I will bring it up to a DM so they can worry about it.
Now I should say that I RARELY ever use my DiveAlert, but in an "emergency" situation I have no qualms about using it. The only times I can recall using it is if I don't have a lobster snare, but someone else in the group does, and I've found a lobster that they don't see. It's all drift diving where I live, so if they miss that lobster it can be a REAL pain to swim against the current back to get that lobster.