Perpetual license - what exactly stays perpetual

[SixChurchStreet]

Subject line might be unclear.

Here's a hypothetical scenario, but a very real one.

Someone buys a perpetual PT12 license with a year of upgrades and support.
Then the following year they extend the upgrade/support plan for an additional year. Then the 3rd year, they like the version they've got running and decide not to renew the update/support plan.

Do they keep the current version they are on, or does that original perpetual license they bought only apply to updates received in that first year, thus knocking the user back to the version they were at a year prior?