Well, sure, Jim -- but "start pondering an exit strategy" and "concession" are very different things. I'd imagine she's been pondering an exit strategy since March, and she might well continue "pondering" all the way until August.
Even if Hillary herself is entirely rational about her prospects, her fanatical supporters are demanding all-out war for the nomination. If she pulls the plug, those fanatics will feel abandoned. Should Hillary decide to try again in 2012 or 2016, she's going to need those fanatics. So her continuation of a campaign that is objectively irrational could be, in a political sense, much more rational than it looks.
Also, keep in mind that campaign debt, a lot of which consists of money that Hillary personally loaned her own campaign. If the DNC and Team Obama don't promise her some kind of repayment, Hillary is unlikely to play nice just for the sake of "party unity."