I suspect it won't - even if AVR started to disappear the Arduino guys have already got a handful of boards out using ARM Cortex M0 and Intel Curie chips. They're quite cleanly integrated with the same IDE and the boards are in roughly similar form factor, so from a dev's perspective if they moved to ARM/Curie completely it wouldn't be too tough I reckon. Not sure if there's any supply chain or manufacturing issues that could complicate things though.