Peyton Manning is irreplaceable. Irreplaceable is a word we use about many players in the NFL, but it really only applies to a handful. Manning makes every single player around him better. His ability to manipulate the pocket and get rid of the ball exceptionally quickly makes his offensive line look better in pass protection, his accuracy and anticipation allows his receivers to flourish in the open field while his presence forces the defense to conceded bodies in the running game. The Broncos do have very talented receiving options, but Manning's ability to negate the impact of the pass rush is something that very few quarterbacks in the NFL have. Even in the best case scenario, the offense would dramatically change its approach if he went down.
BUY
Eli Manning, QB - If you lose Peyton Manning, you're losing one of your most important players. You simply can't afford to trade away valuable assets to address the quarterback position or you will gut your roster. Ideally, you need to buy a quarterback who comes relatively cheap with the upside to be a consistent performer. Eli Manning had a horrendous year last season, but much of that was due to the conditions he played under. Most significantly, Manning played in an offense that forced him to consistently make difficult throws down the field. Entering this season, Manning is expected to be throwing more short and intermediate routes as he is encouraged to get rid of the ball quicker. He probably won't be a top 10 passer, but he also won't come with a top 10 price.
Sam Bradford, QB - Before being injured last season, Sam Bradford threw 14 touchdowns and four interceptions in seven games. He also averaged 241 yards per game. Those are modest numbers, but modest numbers in a horrible situation become much more impressive. The Rams offense was dysfunctional until Zac Stacy got the running game going last year. They weren't built to overcome such a poor running game and that was reflected by their focus on adding pieces to revitalize the running game during the offseason. While the balance in the offense should keep Bradford's numbers from ranking amongst the top 10 in the NFL, he should be consistent if he stays healthy.
HOLD
Demaryius Thomas, WR - The natural reaction to Thomas playing with Osweiler is that his statistics should fall. They likely will, but Thomas led the league in yards after the catch last season and it doesn't take an incredibly talented quarterback to throw a screen pass. Maybe the overall execution of the offense will slacken without Manning, but Thomas should still be a productive receiver so long as his role stays the same. Who knows, he might even get more targets without Manning as the offense tries to rely on more easier throws with a lesser quarterback.
SELL
Montee Ball, RB - As Knowshon Moreno proved last season, it's really nice to be a running back in a Peyton Manning offense. Manning's presence forces the defense to spread out and that creates a numbers advantage between the tackles for the team's running game. Ball is a highly thought of back who has impressive talent, but he's not the kind of back who is going to produce huge numbers in a tougher situation like Eddie Lacy did for the Green Bay Packers last year. Ball is entering the season as a player who rarely gets out of the second round in drafts. His stock will likely never be higher than it will be this season with Manning.
ADD
EJ Manuel, QB - The natural replacement for Manning on the field will be former second round pick Brock Osweiler. However, from a fantasy perspective, Osweiler is essentially an unknown who isn't filling Football Guys' own Cecil Lammey with confidence. Investing in Osweiler is investing the talent around him rather than him individually. If Manning goes down, the free agent wire is likely the best route to replace him. Right now, Teddy Bridgewater is unlikely to be on rosters in a 12-team league, but if he becomes a starter before the season he will likely be selected in most drafts. Instead of trading for someone like Bridgewater, EJ Manuel should prove to be better value as a waiver wire addition. Manuel isn't a great quarterback, but he is surrounded by weapons that should give him easy production and he should be more of a threat with his legs in his second season.
DROP
Cody Latimer, WR - Unless Latimer takes Wes Welker's job before the start of the regular season, then the only reason he should be on your roster in redraft leagues is because you think Manning can maximize his production on limited exposure. If Manning is no longer part of the equation, then Latimer isn't worth carrying on your bench. Without Manning, the Broncos offense would likely focus on getting the ball into the hands of Demaryius Thomas and Emmanuel Sanders, even though Welker's production would likely take a hit also, he's simply too talented to drop from your roster. He could potentially be more appealing as a trade chip rather than a contributor though.