I decided not to renew because we didn’t plan on making any more customisations for awhile, but would this cause those already installed to fail?
They are still installed but the extensions don’t appear in the environment anymore.
No, the expired license will only prevent you from publishing new changes. Your existing, already installed extension is not technically linked to SOD, so it will continue to work even if SOD is not installed.
What can “kill” your extension is time, and Microsoft’s obsoleting and deleting fields and objects. We keep updating SOD, so it always creates valid extensions for the current and next version of Business Central. That’s the main reason it’s a subscription; we are constantly updating it to support whatever Microsoft throws at us.
That’s comparable to a traditional approach where a developer checks every six months that extensions are still valid for the new BC version. Every BC extension needs a maintenance budget to keep up with the ever-changing cloud.
Microsoft sends out email if you have an extension that cannot be upgrades, make sure you have Notification emails set up in Admin Center.