Ravens would never make a deal for Manning. For one thing, they went this route already once with Elvis Grbac and had disastrous results. But also, it runs counter to their organizational philosophy. They build from within, and while they let good players go - Heap, Bart Scott, Kelly Gregg, Jamie Sharper - they don't let their cornerstone franchise players leave - Ogden, Lewis, Reed, Suggs, Ngata. I expect them to lock up Flacco and Rice the same way.
Unfortunately, this probably means they will lose some more good players in the near future (like Yanda, Ben Grubbs, maybe Jarrett Johnson) but they figure they can replace them through the draft, and it's worth the price you pay to let those guys go if it allows you to keep your true blue chip players. That's another thing about the Ravens - because they genuinely believe that every first round pick they make will be a Pro Bowl player that they will have signed to an affordable contract for a good number of years, they won't give up one of those picks for another team's overpriced veteran.