Not only can, but already does he sell it. For example, as recently as in August Japan has signed new deal with Russia about long-term shipments of Sakhalin gas. Russians were caught somewhat unprepared by ferocity of Western sanctions, but not defenseless. Just like the Megarian Psephisma in 432 BC simply had added to increasing tensions between Athenians and Spartans before the Peloponnesian war broke out.