API deprecation on macOS is somewhat overblown. It’s not difficult to get a decades old FOSS Mac app compiling again, and it’s even possible to get projects targeting OS X precursors building with a little effort. Binary compatibility is what gets broken more frequently and is necessary to keep an OS from tripping on its own compatibility hacks.
Should macOS ever lose its terminal and associated capabilities, it’d spur mass migration of users from several STEM fields overnight. It’d be a colossally stupid move that’d destroy a sizable chunk of revenue coming from sales of high-margin and high-spec machines and services that these users buy to use with those machines.