If sentinel is to be maintained post 2015 (and I'm neither arguing for or against that), then presumably something else has to go/give to release the funding to pay for it - or are there still some people out there who still think that more money will be available by 2015?
In the meantime, and I'm not asking for any details, what is the footprint to support the sentinel deployment, admin, supply, engineering, force protection, etc, etc......?