Tebow's not going to lose his job. Not only did the guy still carry a 1-4 team into the divisional round, but considering his popularity, there will be a line of teams waiting to take him off Denver's hands if Denver's stupid enough to try and bench him. Have some forgot the playoff game between Ravens and Patriots? Flacco won with a 10.0 QB passer rating, going on to build a reputation as having the 2nd best winning percentage as a quarterback in his first 4 years. That game Brady also lost with a ~34 QB passer rating. So why would a 2nd year quarterback lose his job considering his accomplishments this season? It's not going to happen no matter what happens tonight and honestly I wouldn't worry about the motivation behind either one of these teams. They are both motivated and ready for different reasons.
The only thing I'm worried about is the Pats got beat by the Steelers, who have been a suspect team all year long after their bye week. Granted they were healthier when the Pats played them, but I think the reason they lost was the bye week. Lots of team lost this year after the bye so I just always wonder about what that does to a playoff team. It sounds like Brady learned his lesson and was really pushing in practice but it can still take you out of your rhythm and the Patriots were really clicking prior to their bye. I hope they managed to maintain that momentum despite the break. If they did, they will be fine.
Having said that I don't think the Patriots need to put additional pressure on themselves just because they are facing the Broncos. This is a good team, despite what people are saying and had they played a full season, their record could have been a lot better. They are not underestimating them. All this team can do is also play like they have nothing to lose either because, honestly, they don't. The only thing they really have to lose is losing itself, like any other team, which sends you home. Nobody wants to go home after working so hard to make it this far, and in front of that crowd, Patriots will be motivated.
All they can do is give it their all and see what happens.