They're pretty much going to have to give up at some point. The west can't feed them with sufficient arms and ammunition to keep up and it has blown through all of its spares. It can ramp up to match, but probably not within the next 2 years which is too late.
Western media has been putting a spin on this in the last week (e.g. blinken's "Ukraine will have to recover some territory through political means"), but it's pretty clear if you look at the production numbers, current shell rates, etc.
It's also why some Republicans are starting to feign being anti-war - to try and make this "Biden's" war, so in the event of failure the failure gets chalked up to him.