Whether they were going to leave or not if it wasn't renewed decades down the road isn't particularly relevant to why Ukraine's economy was in the pits. It's not like those sailors were 'foraging' the countryside for their upkeep.
"It's much like Russia but with no oil or gas" was the better explanation for why it wasn't doing well. It's also why Belarus isn't topping the development indexes.
Do you seriously believe Russians would leave Crimea if Ukrainians didn’t renew the lease?