Depends on what you mean by accepting. They took it as what it was, a loss (though not nearly as bad as Trump's), and were definitely able to see the reasons for it. Obama has always been known to have a good mixture of gravitas and energy but the brought none of those to that ocasion.
As for the next debate, I think last night was mostly because of the person he is, not jus that he came in unprepped (though that was noticeable). If you push his buttons he will get sidetracked, he is not eloquent in a scenario where the audience is silent and simply tries to absorb what he's trying to say (as opposed to people getting fired up in a rally) and quite frankly he just doesn't know his shit about relevant subjects that will always come into play (foreign policy for one). You can't change that overnight.