This has already happened, PC Gaming Wiki has entries for lots of games where support for various old methods of doing things no longer work, on real hardware o

This has already happened, PC Gaming Wiki has entries for lots of games where support for various old methods of doing things no longer work, on real hardware on windows, and you need to use a variety of workarounds like dgvoodoo or a fix by a random third party modder to get the game to operate correctly. And that's before you consider defunct copy protection or trying to add improvements.