If they stay up there for 8 months, that would be about 240 days, which would put them fourth on
this list of longest-duration spaceflights.
The record-holder, cosmonaut
Valeri Polyakov, stayed on the Mir space station for 437 days 18 hours, more than 14 months. That was actually his second stay on Mir; his first stay lasted 240 days. His combined time in space amounted to more than 22 months. He suffered no long-term health issues from his time in space, and lived to be 80 years old.
Other cosmonauts have actually spent longer cumulative time in space on Mir and the ISS, shorter individual stays but more of them. So far as I can tell, none of them have suffered any life-threatening injury due to their long time in space.