My original model AirPort Express has been dedicated to only AirPlay for a long time (the WiFi is even deactivated as much as I can make it it’s connected by Ethernet cable to my AirPort Extreme), I don’t expect it to fail but if it did, I know there are options.
Bluetooth has become much more common for wireless audio receivers and speakers but there are 3rd party WiFi audio receivers. The AirPlay protocol for audio was reverse-engineered long ago and others have been able to make hardware and software that supports it for a long time. Devices like this iDER audio receiver I saw on Amazon are much cheaper than an Apple Airport Express.
I’m not concerned about Apple dropping AirPlay support once AirPlay 2 is done, especially not for audio.