Hello Roy,
Thanks very much for the interest in buying a licence.
Yes -- to confirm Iain's reply (thanks very much as always, Iain) -- a perpetual licence for Hauptwerk allows you to use the major version of Hauptwerk that you purchased (e.g. v5 currently) indefinitely on platforms listed for it in its prerequisites. (If you buy a licence for v5 and you want to continue running v5 50 years from now then that's fine, as long as you still have a computer that can run it, i.e. principally 64-bit Intel/AMD Windows 10, Windows 7, or 64-bit Intel macOS 10.13.6-10.15.) Support for future computer platforms/hardware/operating systems will usually be added in new major versions of Hauptwerk.
Here's an except from the release notice on licence types and upgrades:
For ‘perpetual’ (non-subscription) licenses, upgrades between minor Hauptwerk versions (for example between v5.0.0 and v5.0.1) are free to users with a valid license for v5, but a license upgrade must be purchased to upgrade between major versions (for example between v4 and v5), or between different Hauptwerk editions. All version upgrades are included with subscription licenses (during the period for which the subscription has been paid for).
Best regards, Martin.
Hauptwerk software designer/developer, Milan Digital Audio.