Windows 8 is set to stick around for at least the next five years, but the app ecosystem will begin closing in on itself from this fall.
Microsoft has announced its end-of-life procedures for app submissions and updates for the Windows 8, 8.1, earlier platforms and corresponding Phone platforms. If you can believe or not, developers can still submit new apps to the Windows Store targeting those OS versions, but the last apps will be approved on October 31.
Publishers can continue pushing updates to those platforms. However, Microsoft will end distribution of those updates to Windows Phone 8 and earlier phones on July 1, 2019. Updates will no longer be distributed to Windows 8 and 8.1 devices on July 1, 2023. Apps will supposedly remain existent past those stages in their last updated state.
And all that assumes that the app developer is still working for all that time.
Developers are encouraged to move onto the Universal Windows Platform to develop for all form factors on Windows 10. However, that app landscape has also been struggling to gain ground as users remain reliant on x86 programs and web apps instead.