I heard in dharma talks stories about meditators being so deep in concentration that their heart stops. Is this a risk of deep meditation?  Also, can you get into Jhana and be stuck in the  absorption - as in you are there in bliss for many hours - and if no one disturbs you, would you never come out of it and die?

When you are in deep absorption what pulls you out?

In really deep absorption states you cease to be aware of or care about time passing, BUT, IMO, the level of concentration tends to vary a bit throughout a session, so usually there are at least brief moments where concentration flickers to being a bit less deep long enough to come out of it. Not having that flickering is difficult to achieve, so I wouldn't worry too much about it. Another option is to set an intention to come out after a certain length of time or set a meditation timer with a bell (Even hard jhana folks like Ajahn Brahm claim this can reach you in deep jhana states, with few exceptions that are really extraordinary cases). Worst case, you just come out of it when you do, usually after a few hours. But it doesn't last indefinitely.

No, you do not need to worry that your heart will stop or that you will die from meditation. I've been meditating for many, many years and never had this kind of problem, nor have any of my mediation friends who've been practicing for similarly long periods of time.

Eventually I have to go to the bathroom.

This. Or a cat jumps on me impatiently and howls. Or the body runs out of the neurotransmittors needed to maintain the state.