Like others have said, he can stay in Hong Kong until his visa expires, and if he is physically present in Hong Kong, there is nothing forcing him to leave if he chooses to stay illegally or if he finds another legal means to get a visa (though it sounds like his chances are low).
There can be many reasons why you may be unhappy with this situation. You should never feel endangered, though, and if you need some advice to help deal with the situation (maybe legal or for yourself and mind), there is help... Please do reach out to one of these organizations and explain the situation and see if they can help you, because it seems he may be staying in Hong Kong:
https://www.womencentre.org.hk/En/Se...womenhelpline/
https://www.whwhk.org/
https://www.swd.gov.hk/en/index/site...ofserv/id_230/
https://womencentre.org.hk/En/Services/
And again Po Leung Kuk is a big organization which helps people:
http://family.poleungkuk.org.hk/en/page.aspx?pageid=873
does a sponsor gets implicated in a visa overstay situation ?