Too much of the TO debate is polarized. Love him or hate him, he will probably be with us at least another year. Furthermore, given how much Jerry likes him (TO basically ran Parcells out of town) he may very well play out his contract.
The truth of the matter is that everyone's performance begins to fade over time. It is actually more or less imprinted in our DNA - has to do with errors of replication at the ends of the molecule. People love to bring up Jerry Rice but he had his last truly dominant season (as measured by Rice's career peak) in something like 1995 at the age of 33. He would play 9 more years and would break 1000 yards four more times but he would never get more than 1300 yards in a season, never had more than 10 TDs in a season and never averaged more than 15 ypc in a season. After 2 sub 1000-yard seasons in SF his career was somewhat reclaimed when he went to the Raiders with a more balanced attack with Tim Brown playing opposite to him. He was no longer a true elite #1 WR but he could function effectively as a co-#1 for a few more years with Charlie Garner and Kauffman providing the complimentary ground threat. I think this is the same transition we hope to achieve with TO and RW11/Felix/Choice - TO cannot continue to be the focal point of the offense but he can continue to be a dangerous WR that the defense needs to account for.