The thing with anti-virus software that you have to subscribe to is that the software will download (usually) daily updates, so it covers the latest threats.
If you no longer have a subscription, then what you have already on your machine is what you will be left with and any future threats wont be picked up.
I would get in contact with McAfee as, sometimes, a subscription purchased will come with more than one license - meaning, if it came with two or three licenses, you could put the same license onto both machines.
Leaving these things to chance, or only leaving it to a free anti-virus software is a bit too dangerous for my liking