I wouldn't consider Bennett worth a roster spot at all. If you really believe the both Staley and the Bus are going to be riding the cart, then I'd take a shot on Willie Parker. Hes's fast, elusive and did well in limited time last week.
Death awaits you all, with nasty sharp pointy teeth
If Bus were to get injured along with Staley, I guess they could either go with the FB Haynes who has been doing well with limited carries or the rookie Willie Parker. As long as that oline is healthy, they should get solid production from a capable back. Tough call really. I'd lean towards it being Haynes or a committee approach with Haynes/Parker til someone got hot.