Nokia Developer/Publisher support told me he should ask my question here.
On Symbian it's not possible the close WhatsApp by default, only 3rd party taskmanagers or app killers can end it. (e.g. androtaskman, JBak, KillMe)
Will Nokia QA accept an little app which:
- has no UI
- closes the related processes with Qt/native C++ mix (a Qt function with TFindProcess, RProcess etc.)
- shows a CAknConfirmationNote like "Successfully closed WhatsApp"
- needs PowerMgmt Capability