The absolute best they can hope for by the end of the year if everything goes amazingly well would be to reach the coast via their current salient and thoroughly establishing themselves, cutting off the land bridge to Crimea and the rest of Russia’s forces South of Kherson.
I don’t expect this to happen at this point unfortunately, but that’s what they’re trying to accomplish.
To be clear, Crimea itself is not a location they could hope to take back by force without a gigantic increase in the size and loadout of every branch of their military, think of it as a fortress whose land bridge is barely passable, and heavily fortified.
A much better strategy, which they’re going for, is to try to cut Crimea off from Russia as much as possible and keep them besieged, while they restore their pre-2022 borders to the east.
I have no idea how they intend to eventually retake Crimea, unfortunately at the current stage that seems like wishful thinking. But perhaps if they can take back and hold the rest of their territory, which isn’t unrealistic at all, they could slowly, very slowly, amass the required resources to attempt such a difficult campaign.
What the Russians would be doing with that time… I don’t know. Surely continuing to press the borders, bomb cities, and shore up Crimean defences.
I see no end to this war in the coming years, unfortunately. Not without compromise from one side, and neither wish to compromise (not that I’m suggesting they should, just observation).