Android Lollipop represents less than 1% of the total number of Android devices. Every year on average, Google drops support for a version of Android.

No Google Play updates absolutely doesn't mean that the device will stop working, it only means that some apps may decide to drop support for Android Lollipop for their new version if they want to use the newer version of Play Services (but some apps don't use Play Services and some could stick with the older version). I personally plan to keep supporting Lollipop in my apps for at least a year or two.

And even when developers will eventually move on, these phones will still be able to download and run older versions of the apps for a while.