I fear the problem is that Ukraine can't of course cut all of the supply lines without actually gaining all the land around crimea and still some supplies would get through. And as human cost is no coat in russia, they don't care what kind of hell Crimea would be. In WW2 Sevastopol was under actual siege and it held 2-3 years if I remember correctly.
My understanding is still that Ukraine haven't done bigger mobilization so I don't know if they have mon power to do actuall ground attack even against much weaker troops? Manoeuvring war has largelly stopped because of drones, Ukraine would need to still push through heavily fortified area, which for sure is mined and under constant drone thread. It is not easy task, but as I said, I hope Ukraine proves everyone wrong here!