nasa.gov:
NASA astronaut Frank Rubio holds the single spaceflight record at 371 days.
The length of their stay at the station was unintended but it wasn't a record. Were they going to run out of oxygen or other supplies that threatened their lives?
I really don't know...I'm just going on comments others have made that are more knowledgeable about this stuff than I am, that there could be serious effects for that long a period up there. Hopefully that's not the case.
I'm just glad they're finally making it back. I sure as hell wouldn't have wanted to be stranded up there all this time.