The official game page for Super Soccer on the Switch Online Super Nintendo service notes how this title will be removed from this digital game library on 27th March 2025 (or 28th March, depending on your location). The title is listed as a Spike Chunsoft release.
Nintendo: “This game will no longer be available starting 3/27/25 at 6:00 p.m. PDT.”
From another article (linked in above article), talking about Famicom version:
Nintendo: “The title “Super Formation Soccer” (Spike Chunsoft) included in “Super Famicom Nintendo Switch Online” will end distribution at 10:00 AM on Friday, March 28, 2025. After distribution ends, even those who have already downloaded “Super Famicom Nintendo Switch Online” will no longer be able to use it.”
For a game like this, I believe you are correct. Let’s see if this is one off or they start removing games regularly.
I think they will announce the date in April direct. fingers crossed