I wouldn't call his 2 years here a turn around yet or describe it as "quite remarkable". The turn-around from the beginning of this year is extremely impressive. However C-USA without Houston, UCF and Memphis, was significantly weaker (C-USA went from #8-#11th RPI under DW to now 13th). I wasn't happy with DW and I'm very happy with Manning. However, the program hasn't been turned around yet. The work has just begun. If Manning leaves now, it puts TU in a very difficult spot.
This is not what a turnaround looks like:
2010-11: 19-13 (11-5; lost in C-USA semi-final; C-USA #11 RPI)
2011-12: 17-14 (10-6; lost in C-USA quarter-final; C-USA #8 RPI)
2012-13: 17-16 (8-8; lost to #20 Mem in C-USA semi-final; CBI first round loss; C-USA #11 RPI)
2013-14: 21-13 (13-3; won C-USA tournament - all against the weakest C-USA in years: C-USA #13 RPI)
So far, this is more of the same outside of one outstanding C-USA tournament run by Manning (Which was awesome). I understand the difference between making the tournament and not is huge. However, C-USA was awful this year. Next year, Manning would face a much more difficult task in the AAC. It seems like he is going to bolt at the first opportunity and avoid that potential pitfall (somewhat similar to Graham leaving the year before TU had to face OSU, OU & Boise St in the first month).