The Hilton website does not use the term expire. Here is what the terms and conditions say.
Members who do not have eligible activity as defined in a. - d. below in any 24 consecutive month period may be removed from the Program and are subject to forfeiture of all accumulated Points. At the discretion of Hilton Honors, such Members may be permitted to remain in the Program and removed after five years of inactivity. To keep accumulated Hilton Honors Points, the Member must take one of the following actions within a 24 consecutive month period: (a) stay at a hotel within the Hilton Portfolio pursuant to the terms herein; (b) earn Hilton Honors Points through any third party source of Hilton Honors Point accumulation, including a Hilton co-branded credit card, pursuant to its terms; (c) purchase Hilton Honors Points; or, (d) donate Points through The Hilton Honors Giving Back Program.
Failure to take action (a), (b), (c) or (d) described above will result in the forfeiture of all accumulated Points and, after five years of inactivity, to deactivation of the Member's account. Once the Points have been forfeited, the Member may not retrieve any forfeited Points but Member may begin to earn Points again thereafter. Any Reward redeemed by the Member before the Points are forfeited (such as a hotel reservation made or a car rental voucher obtained) is still valid. This applies to any year of enrollment, including without limitation, the first year of enrollment. Members who fail to pay mortgage related payments properly due and owed to Hilton Grand Vacations®, including but not limited to principal payments, interest payments, late fees, and service fees are subject to forfeiture of Points equal to the amount of Points accumulated in connection with Hilton Grand Vacations®. Further, Members who fail to pay amounts due to Hilton Grand Vacations® are subject to forfeiture of any Elite tier status earned through Hilton Grand Vacations®.