If this happens, it will break medical devices and cause physical harm. Specifically CGM’s (Continuous Glucose Monitors) not compatible with iOS 26 where this data is ingested into insulin pumps every minute and automatically inject insulin every five minutes for Type 1 diabetics.
By far the largest problem I've had is that if you move from region to region (I just escaped the USA back to the UK), there's a complication between subscriptions and regional stores.
You can't switch your region while you have an active subscription - which includes any AppleCare or other long-term (1 year, say) "subscriptions".
Applications like Glucose monitors and Diabetic Pump controllers are distinct between regional stores - a UK pump won't work with US software and vice versa, at least for Tandem.
So I had to wait for the subscription to time out. Cancelling it just means you don't pay on the anniversary, it's still active, and calling Apple support wasn't useful - they tried to help but ultimately couldn't effect any change.
Fortunately my last subscription timed out this month, and I can now use my UK pump with the UK software, linking to the UK hospital systems.
So, just beware if you move continent - you might want to make sure you time it well regarding any Apple subscriptions, which didn't occur to me before I moved.
