They aren't doing the free upgrade to 10 offer anymore so you're probably fine. I've been running a 7 instance in a VM for a long time and never had a problem with it upgrading to 10.
Do not assume that the "Free" expiration stops them from loading 10 in all but name & fugly menu on your back-end through 40+ supposed updates & patches. The telemetry is what they are after, the telemetry is what they will go to almost any length to collect and telemetry is all you are good for... at the moment.
