I'm not sure that's why it's being done. The Senator or Delegate proposing the legislation doesn't have to stay anyway (Del Ivey noped out of there immediately after presenting his bill Tuesday at 2am) and many of them have other hearings throughout the day that they have to leave for.
Even if they stay, there's no guarantee they'll listen (afaik Del Dumais was on her phone the entire time people were testifying against her bill).
Personally, I wish there was a rule that required them to stay, maybe would cut down on some of the 'legislation for legislation's sake' as it were.
The committee however, will stay for the whole thing. I'm not sure what the requirements there are, but just leaving when there's still testimony if there's not some sort of emergency is just not done, according to MGA veteran staffers I know. They are there to hear your concerns, and from my experience they give the job at least that much respect. You will see them eating at the desk for these hearings, its just expected of them to be there as part of being on the committee.
For instance, House Judiciary committee chair (Del. Clippinger) was there almost the whole time on Monday/Tuesday for the 18-hour hearing, and from what I heard he was nothing short of respectful and courteous the entire time.
It was my first time, but I saw a lot of empty chairs Monday night. Some come, go, come back (longer than potty breaks)...others were never there.