People buy computers to run software. If they can't run their existing software on it, the computer has no value. Just like with the original PPC-to-Intel transition, where Apple provided a PPC emulator on Intel, if they go with ARM, Apple will have to provide Intel-to-ARM translation software in macOS for several years.
But now, a significant number people are using Macs as hosts for x86 Linux and Windows virtual machines. This changes the calculus a bit. It's one thing to emulate an ISA to run software in a user context; quite another to perform cross-ISA virtualization. QEMU can do the latter, but at a significant performance penalty.
It should also be noted that Apple is sitting on _much_ more cash than Intel. At the end of last year, Intel had $14B in cash on hand, while Apple had $285B.