Warner is now signed through his age 39 season. However good Warner was in 2008, and he was very good, precipitous decline is any snap away and incremental decline is every snap away. He's still a great quarterback. Arizona must make sure their line can keep him that way.
The next step, presumably, is to trade Matt Leinart. Leinart is signed through 2011 and has made some noise about being traded. He's a Buc. It makes too much sense for him to land anywhere else. Tampa has a ton of cap room to absorb Leinart's rather reasonable contract (counting $2.6 million against the cap in 2009 and $4.0 million in 2010) and no quarterback to speak of. Tampa could even restructure his deal, front loading it while simultaneously making it easier to cut him should he struggle.
Arizona keeps its Super Bowl quarterback and adds something like a second round pick. Not bad.