they will not start but you can force them into the game once you start.
I had my Wazzu RB get injured in week 4 for a 3 week rib injury, after those 3 weeks he was questionable for 4 weeks. the last 2 of those 4 weeks I was forcing him into the game because I had no run game without him(although I didn't really have a great run game with him but it kept users honest). that put me into week 12 where he was probable and then in week 13's bye he was still probable, in fact he didn't come off the injury report until conference championships which I was not in... oh and then he got re-injured on the first drive of my user v user bowl game.
sorta the same thing with my QB, Tuel went down in week 7 for 2 weeks, he spent 4 weeks as questionable and 2 weeks as probable. he got re-injured late in my user v user bowl game as well but only for 1 drive...