I'm in a similar situation...I'm planning on reapplying in the summer for the World or Prem card...though I'm currently using the Platinum card to keep my miles from expiring...and if I cancel the Plat to apply for the World, I wonder what would happen to my miles in the meantime...

I know that the mileage bonuses "may not available to current account holders". If you cancel and reapply for a different card, are you still a current account holder?? Since the bank doesn't run the FFP and vice-versa, I imagine there's a fair bit of grey area...probably not to the consumer's advantage.

On the topic of the companion ticket, do you know anything about it? I posted a question not long ago about it and didn't get much of a response...there was the question about how the companion ticket has to be booked into H, but according to the fine print, it can be booked based on any economy fare class...a bit of a contradiction.

Good luck swy!