It would be cool to have the RAD working as a standalone app BUT, it would be very time consuming, because the RAD developer would be himself doing a lot of things that are already included in C::B.
As real life examples see:
-DialogBlocks: It is a standalone app, but as time has passed, Julian had to make it almost like an IDE to be more usable (it haves a code editor, generates MSVC projects, compile and debugs programs), so at the end is like having an IDE inside the RAD
(instead of having a RAD inside the IDE ).
-MFC editor from MSVC: It doesn't come as a standalone app, for the same reason avobe.
So at first having the RAD as a standalone app appears to be ok, but as the time passes the RAD developer would be implementing all the things an IDE haves.
IMHO in the situation that makes sense to have a standalone RAD is in a XRC only resource editor.