I don't see Witten as a progress stopper at all. He still is productive in the passing game and his blocking is still very good. Not only that, but it is clear he is a leader...so much so that when Dez would melt down he would get after him on the sideline. His production is still fine, 7th in receptions for TEs last year, with a predominantly run first team. He will be the 9th highest paid TE, getting less than such greats as Trey Burton and Charles Clay.
Witten is the least of our worries.