Interesting Q about Witten. Would be cool. Frankly I was surprised he came back. He missed football I guess and calling games for TV wasn't his thing.
I don't think 3 more years is crazy at all. I think it would have been very likely if he hadn't taken that year off. That would make next year the third, instead of the year after. I expect his production to drop and for him to play less. Only three receptions against the Giants last game. That will not get the job done, but it doesn't miss by much. So assuming he can stay healthy and wants to play three more years and is productive enough for the Cowboys to give him that contract, I'd say it could happen.
Needs 170 receptions to tie. 15 more games this year and 16 the next two - that doesn't count possible (likely?) postseason. That's averaging just 3.61 receptions per game to tie.