If your permanent residency card is expired for all Russia knows you might not still be a permanent resident. You could have abandoned your residency. H
w would Russia know? If you have no proof of permanent residency you'll have to apply for a visa in your home country, the UK in this case. In addition, if you are a permanent resident you'll almost certainly need to present an unexpired permanent residency card when entering the US. So, regardless of whether or not you plan on going to Russia (or anywhere else) you really should renew your card.