Hooker lost his nerve and went on the defense, however up until this point he was still making coherent and logical, albeit cautious, decisions.
If Sickles holds Hazel Grove, the battle really cannot be won by Lee unless Longstreet comes up.
Chancellorsville could turn into even more of a meat grinder than it was, which of course would benefit Hooker. Lee still suffered high casualties even in a decisive win. If it turns into a stalemate where the Union has the artillery edge, which Hazel Grove allows them to, and Sedgwick comes up, Lee either fights and sees half of his army disintegrated in bloody fighting, or he retreats.
Hooker for all we know could have regained his nerve without being concussed and with some defensive success, which Sickles could have provided, he might be emboldened to go back on the attack, in which case, Lee is fucked until Longstreet gets there, and of course, Longstreet won't be there at least until the 9th.
I think Lee could have executed a very successful withdrawal, as he showed he could in 1864, but you really have to wonder if Hooker is able to push him back, link up with Sedgewick, and get Lee to have to fight on open ground if his army is going to survive the encounter. Lee had not yet fully learned the lessons of Gettysburg about entrenchment.
Of course, a Confederate loss that leads to Jackson somehow surviving could have any myriad of effects.