To be honest, fully panicking diver probably won't have the rational thought to swim to you and grab your reg, chances are he'll just bolt.
If a diver isn't panicking he may still just ascend too quickly. I've seen a lot of divers with no problems at all just ascending way too quickly after a dive (which is insane to me, but it's just the reality of diving with basic divers sometimes). I wouldn't want to be dragged up by someone who's otherwise calm, but ascends too quickly with them out of reach.
If a diver isn't panicking he may still just ascend too quickly. I've seen a lot of divers with no problems at all just ascending way too quickly after a dive (which is insane to me, but it's just the reality of diving with basic divers sometimes). I wouldn't want to be dragged up by someone who's otherwise calm, but ascends too quickly with them out of reach.