For him to be punished for war crimes would mean he'd have to be overthrown from Presidency in Russia. The only way that will happen is if there's a coup.
Realistically Putin will never be tried for war crimes. If there ever was a coup in Russia, he'd more than likely be executed by his own people.
Guess he's stuck never leaving Russia then. Despite the fact foreign heads of state, members of government have various immunities, I hope they'd make an exception for his case if he stepped out of the country.