Regarding the Rode K2, NT4/5's and Classic II, I'd most definitely keep using them no matter what other microphones I had. They can, and often do, win over much more expensive as well as highly sought after microphones.
For the NT1000/2000 and such, chances are I'd eventually stop using them unless I ran out of other mics.
Speaking of the NT1A, NT3 etc, I'd probably stop using them very early on as soon as I had any other decent mics available.