Just so we can put this to bed
In 2010 foster had 2220 yards and 18 tds in 16 games on 327 carries
In 2011 foster had 1841 yards and 12 tds in 13 games on 278 carries
In 2012 foster had 1641 yards and 17 tds in 16 games. This was his high water mark for carries with 351.
In 2013 foster had 725 yards and 2 tds in 8 games.
In 2014 foster had 1573 yards and 13 tds in 13 games on 260 carries. He was the number one rb in fantasy ppg and number 5 in total points.
In the 2015 offseason, he hurt his groin and had preseason sports hernia season that was supposed to keep him out until mid october. The owner who would later release foster started saying negative things about him in the press. Foster missed just 3 games and had 8 rushes for 10 yards and 3 catches for 25 in his debut. Yuck. The next week? 19 for 41 rushing and 9 for 77 receiving. Then 18 for 53 and 5 for 59 receiving with a td. Then 18 for 59 and a td plus 5 for 66 receiving and a second td. It was on his 18th carry - actually a bunch of consecutive carries at the end of a blowout - that foster got hurt, because BoB apparently wanted to run him back into shape.
Remember that the prior season he averaged 4.8 yards per carry and was literally the best back in fantasy football per game.
So in the 4 games he came back early from sports hernia surgery, where he had a disappointing 390 total yards and 3 tds in 4 games and his ypc increased every single week while he averaged over 8 yards per catch each week. I reject the idea that he had just suddenly fallen off the cliff.
The bigger question is whether he's healthy right now. If he came back anything close to full speed it will be better than what he was last year, and the dolphins aren't acting like he's slowed down. But he did have an achilles tear, and that's a nasty injury. If you're interested in reading, here's an interesting article on the injury and return to performance
http://www.dynastytradecalculator.com/arian-foster.html
Tldr - he still has literally number one overall player upside. And he still could get injured before the season and be worth nothing.