Ukraine has lost. They are not getting their separatist regions back.
Their choices are to keep fighting, which will not change this outcome, or negotiate an end to the war so they can stop dying and start rebuilding. Their negotiating position will only weaken as the war continues absent some one-in-a-million stroke of luck.
This isn’t “I kick you and you don’t defend yourself.” It’s “I kick you, you defend yourself, lose, and choose to either walk away or keep getting beaten up.” And that’s not even digging into the actual causes of the war, which are nowhere near as clear cut as Russia one day waking up and deciding to attack out of the blue.