Yes, that's what Hilton can do - under the Abbreviated Terms and Conditions:

“7. Members who do not earn points in any six month period may be removed from the active membership list. Members who do not earn any points in any consecutive twelve month period may be removed from membership in the program unless a member reactivates under terms and conditions as may be established by Hilton HHonors Worldwide, LLC. Failure to reactivate will result in a member’s account and forfeiture of all accumulated points.”

Any qualifying activity - points earned with partners, such as USA Today subscriptions, etc. will count for activity. Using points will probably as well, but that is my opinion, as I did not look this up.

HHonors will attempt to notify you - but I see one major caveat - if you have not been active for six months, and you are removed from the active membership list, you may be discontinued from e-mails, etc. and may miss the all-important announcement. Think of this: these programs are affinity programs designed to reward good customers, meaning those who stay frequently; eliminating accrued miles held by inactive members reduces Hilton's liability for granting awards, therefore is good for the bottom line.

In fact, they often - but I would not count on this - notify you after 14 months or so, and give you a bit of a chance to carry out some qualifying activity. This has happened to two people I know, but I would not count on leniency myself. It really pays to read the Terms and Conditions - in fact, print a set out for your visits to Hilton family properties - and to review your account quarterly, of ANY affinity or award program you belong to, as Terms and Conditions do change.

Cheers.