The 6 points BackdoorBandit made are correct.
1: People have been bypassed (some due to the Q400 18 month rule)
2: If they do not have the minimums they legally can not be Captain
3: A 300hr FO flying 800hrs a year (/2 for CO-Pilot hrs) would take 3 and a bit years for the 1500hrs for an ATPL.
4: The Company will simply go down the seniority list until they hit the next qualified candidate with a bid.
5: The Company would be silly not to recruit guys able to fill Captain seats.
6: If your options are flying a Chieftain or a Dash-8, I know what I would choose.