If the idea is to have one helicopter type to replace the rotary wing assets and cover the King Air missions with fewer total aircraft then perhaps the AW139 makes sense.
Can the King Airs land on the beach at Barra?
I can see where you are coming from, but surely the AW139 is on the larger end of scale for this task.
I cant see them ditching the King-Airs in a hurry. I would still put money on then looking to upgrade the EC135 fleet.