I would be surprised if any of the Invincable class ends up being sunk in an exercise. Sinking ships that size would be sensative with the increasingly strong UK green lobby.
I think the MOD will at least try and sell one of the class as a helicopter carrier with Ark Royal being retained as a backup for Ocean albeit minus her ski jump. The remaining hull being stripped for parts to keep her sisters going before being scrapped out.
I agree that the Invincable class would be a difficult sell considering their heavy life but I think the Ark will be retained longer considering she has gone through two deep refits in recent years and now favours the commando assault carrier role.