Them capturing back all lost territories including Crimea is possible but unlikely and to be frank I have hard time taking seriously someone presenting themselves as some kind of an expert on the subject matter who refuses to admit this. There's an acceptable amount of losses for both sides and negotiations wont start untill either side reaches a line after which the casualties becomes untolerable compared to the gains they're making. Russia can probably keep throwing their poor farmers into the meat grinder for much longer than Ukraine can. This is not especially relevant yet but unless some big break through is in the horizon it might be something people need to seriously start discussing in the somewhat near future.

Also I'm not a military expert either so what do I know. This just seems like the most honest assesment of the situation right now.