If the Broncos can't sign Manning, Denver will, long story short, be in trouble.
They have many needs and haven't addressed many because they are waiting for Manning's decision.
Also, Tebowmania will have a huge impact on the Broncos. Denver can try to trade the former Florida Gator and hope for a high draft pick, or the Broncos can ride it out with the unconventional celebrity.
With a full offseason, Tebow may be successful in 2012. Tebow racked up wins last season, played at a par level, if not worse.
The Broncos could spend an early pick on a quarterback; possibly even their first. QB Ryan Tannehill's stock has been rising at an incredible rate and will likely be taken within the first twenty picks, so the Broncos should look elsewhere.
Denver, however, might want to overdraft a quarterback to insure that the franchise acquires whoever that may be. That quarterback will compete with Tebow for the starting job.