I can surely buy that he had to drop him off at that point, but after he deactivates HAL, why doesn't he look for him again? Frank surely couldn't have gone far with no gravity around.
Uh, the dude was flailing around clutching at a loose hose in deep space!
Under those circumstances, it's very, very, VERY safe to assume that if he stops moving around he's dead. Death comes very quickly if anything goes wrong in deep space, and IMHO he kept moving for an unrealistically long time.
Only shows him moving for about 20 sec. Not really unrealistic IMO. But you're right about him being dead by the time Dave gets to him. The loose hoses are very visible.
If that had been an air hose he'd have been dead a lot sooner than twenty seconds! But maybe it was an electrical cord that kept his suit heated, that would kill him soon enough in an environment that's about one degree above absolute zero.
But he was dead, dead, dead, and Dave knew it. He just couldn't let a comrade go without trying to do something for him.
I remember in the old IMDB days all the debate as to how realistic the scene with Dave blowing the pod hatch to enter the airlock of the Discovery. At least some sources say it's possible.
Anyway here's an article I thought you might like: