By the time the boyonett charge was made, it was already late in the day. Oh they could have taken the hill had the 20th Maine faltered, but anything else would have to be done on the next day.
If they consolidated the position at night, it's quite possible day 3's fighting would be centered on the Round Top's again and Pickett's division would be sent to reinforce it, butterflying away the disasterous charge.
Meade would almost have to attack at that point too, which would only favor the rebels. Not to mention Union morale at that point was low... and the rebels had just proven again, they can attack any Union position and defeat it. That would be more devastating than any losses took that day.
Not that it's going to win the war by any means, Lee just doesn't have the means to stay in Pennsylvania indefinitely.