I'm reasonably sure the HOIIV DLC team is separate from the game development team, similar to how CK2 and EUIV still get DLC even while HOIIV was being developed.
The game was developed by a core team of six people, I believe; with some people helping out when needed. These are not the massive undertakings we know from the AAA gaming industry. It might be that one or two have moved to something else by now, but it is just as likely that the same people are working on the upcoming patch and future DLC.
Still: there are people unacounted for, according to some posts around here. Regardless, I take it pretty much as a given that they are working on something new.