You don't know that he won't be. We know a new writer is about to be announced, since Duggan's run ends in July. Safe to assume a new #1 will be out...
I didn't know Kitty and Carol were particularly close... but surely that guard ought to have recognised the name as being that of Ms./Captain Marvel?...
No, she doesn't have a codename in the MCU. The only other name she's used is Lieutenant Trouble, because the first Captain Marvel film which was set...