Hi, Ritak. As a concerned parent, you have every right to be concerned about your daughter. I'm a father with a grown daughter, so I can very much relate.
To answer your question:
Having a relationship with a bipolar always poses special challenges, and in this sense your daughter is bound to experience emotional hurt. Physical hurt is far more remote - about the same as if your daughter were dating a so-called "normal" person. If the person your daughter is dating has a drinking or drug problem then the risk for emotional or physical hurt goes way up (this also applies to "normal" people with drinking and drug problems).
As to the risk if he goes off his meds: Meds are only part of the treatment/management equation. The boyfriend also needs to be sticking to regular sleep patterns, be mindful of stress and whatever triggers may set him off, and stick to healthy lifestyle routines.
In certain situations, going off meds (in consultation with one's doctor) may be acceptable, but only if the illness management routines are firmly in place.
So, yes, your daughter will face a lot of hurt if the boyfriend is negligent in managing his illness. By all means, feel free to give your daughter the third degree in this regard, but also temper it with some good things to say about the boyfriend.
The upside to dating someone with bipolar is that chances are your daughter has found a very sensitive and caring person who makes her feel cherished and very happy. Bipolars can also be very high achievers, who are well-placed to provide the material as well as emotional security for your daughter.
Finally, keep in mind that if the relationship fails it will probably have nothing to do with the fact that the boyfriend happens to be bipolar. It will be the usual stuff - the chemistry isn't right, too many differences to overcome, etc.
But if he is "the one," and for all the right reasons, you have every reason to be happy. Yes, there will be obstacles, but they are ones that two mature adults can easily work with.
Hope this helps -