Apple has always had a multi supplier strategy. They also used Samsung at 1 point (and still do). It's whatever works at Apple so no difference. They'd eagerly switch as needed.
Not sure how many producers have the available long term supply to meet Apple's demand. Samsung might already have contractual obligations for their short term supply with other manufacturers so it might not quite be as straightforward as just switching overnight.
Intel has already puts its arms up for ARM production as well.
Probably not at the process sizes or quantities Apple's buying up anytime soon, though.