Yep, the M1P and Spark I own haven't had (or needed) an update for maybe a year or two now.
They still fly perfectly.
There's a point when updates are very scarce once all the bugs are flattened, then it's just as simple as stop making parts, consumables like batteries, or indeed even offering a repair service / tech support.
It seems it is the loss of batteries mostly that makes the drone eventually unserviceable.
Usually the likes of MAS props are made for most drones, though I'm sure eventually they might remove props for really old models when it's no longer viable to make them in decent numbers, and give them a little warehouse space.
As we know, it's not just DJI making drones obsolete . . . some places like the UK with their upcoming rule charges, and the US with RID might cause some to become unusable (although RID modules can be used).