Considering they've even gotten away with breaking the rules (custom ISA extensions), I imagine nothing ARM does could realistically cause Apple to be unable to continue manufacturing ARM-compatible chips.
Yeah, turns out when you're one of the founders of ARM you get a pretty broad license!
I would imagine that Apple (which put money into Acorn and ARM JVs over thirty years ago and I think was the first third-party company to do so, by a very wide margin) has a much older license than anybody else.
Does that also include access to new versions of ARM not yet released?