This now redirects to a casino site. I asked ListMyCDs.com (who is a Finn) to have a look, and he said:

Seems the society running the site haven't been having any activity for years. We have a law that societies need to update their yearly financial data and info about people responsible for running it to public registry and there's zero updates for years now.

Wikipedia page https://fi.wikipedia.org/wiki/Populaarimusiikin_museo has "Kadonnut verkosta kesällä 2022, jotakin on tapahtunut mutta mitä?" which could be translated as "Disappeared from the web during summer 2022, something happened but what?". There's also facebook discussions from 2022 confirming it's during the summer 2022 but no exact date.

Also based on this, domain expired during the summer, updated July 2022: https://web.archive.org/web/20220705144643/http://pomus.net/
Domain has been having a new owner since 29.8.2022.

Given this, it seems unlikely it's ever coming back, and marking the links as ended while dropping any specific handling code seems sensible enough. We will probably need to keep a basic amount of code to mark it still as acceptable under other databases so that the existing ended links don't show up as errors.