Tom Brady
Never took a stud QB early (usually I'm 10th-12th in the league taking one, and make the playoffs nearly every year). No backup; hopefully, I'll figure out who my Week 8 bye QB will be sometime in the next couple months...but no Plan B, so he better hold up.
HOWEVER...I think most folks who have been doing this for awhile can truthfully no one is make or break player. You do this long enough and pretty much everyone has had this kind of thing happen:
lost Javon Walker for the entire 2005 season (#1 WR) but still took the league title
won a Super Bowl in 2006 with a QBBC of rookies Jay Cutler and Vince Young
won a SB with a WW QB (Kurt Warner, 2007)
made the final four in 2008 with Addai and Edwards as the 1st two draft picksASIDE: No repeats; different titles in mulitple leagues
None of those seasons were especially extraordinary, and there were lots of failures and misses mixed in with those gems.
Point being that while in late August/early September we think one or two players hold the key to our season, FF mirrors life in that it often turns out far different than we initially planned. But when you work hard, scour the waiver wire, and make a few savvy trades...things have a way of working out...often with different outcomes than what we predicted, but nonetheless quite pleasant (and profitable).
Don't get discouraged if the linchpin of your season fails. There is often another way you may have previously overlooked.