They claim enough of Rosetta will continue to exist for games and things like wine to work. I suspect the main thing they want to kill off are all the x86 slices in the mach-o fat binaries for all of the frameworks.
My source is I know how they handled Intel 32-bit support for Wine the last time they deprecated it. They went out of their way to keep codeweavers happy even though they let all the 32bit games on steam straight up die.