Running backs are a dime a dozen in the draft. For example Alex Collins, Spencer Ware, and Chris Carson all had 900 + yard seasons in the NFL and have served as every down running backs at one time or another. I think the highest draft capital we spent on these players was a 5th.
Gurley, quite frankly I've never been that impressed by even when he was healthy. He is a bit like Penny in that he is a patient runner, and he isn't going to break too many tackles. He also ran behind one of the best lines in the NFL when he was running all over the league. He can catch and pass block which is a plus -- but at this point he'd be an expensive third down back for us. His days of being a feature back are all but done with his knee problems.
The draft is where we need to look in all honesty. We need another bruising running back to step in if Carson can't go, which at this point has been more often than not in his career (is out with an injury almost every year). Penny won't be available for half a year, and he really doesn't cover the same niche as Carson.