The S-63 UserPermit for OpenCPN is valid as long your copies are running on some machine.
There are several copies allowed, so the fee is one-time just to cover the administration costs.
As the IHO S-63 standard mandates, a UserPermit is always only valid for "one system" - a combination of Hardware
. Charts licensed for OpenCPN will not run on an ECDIS system and the Admiralty/PRIMAR/Transas/Chartworld sets of the vessel can't be used by OpenCPN or MaxSea
In general S-63 charts are licensed for a period - max. one year - during which you are receiving or can request updates.
LINZ will go most probably to fortnightly updates likewise the Australian AHS.
Once the license
period expired charts will stay on the machine.
We did run tests last summer (Europe) on several OpenCPN systems without issues.