They get slaughtered. Uriah among them. Joab, no doubt suspicious, an enabler and facilitator to the cover-up, if not the king's indiscretion, sends two Messengers to David with the news of the gory defeat. And Joab is right. David's response to Uriah's murder and the slaughter of his regiment though faked with anger and fury is, in reality, relief.
Some people live.
Some people die. Nothing we can do about it. David no long bears the burden. The truth is concealed. The guilt and responsibility passed.