What would happen if you've created some processes that subsequently made themselves daemons (i.e. called procmgr_daemon())? As we mentioned above, the wait*() functions and sigwaitinfo() won't help.
For these you can give the kernel an event, such as one containing a pulse, and have the kernel deliver that pulse to you whenever a daemon terminates. This request for notification is done by calling procmgr_event_notify() with PROCMGR_EVENT_DAEMON_DEATH in flags.
See the documentation for procmgr_event_notify() for an example that uses this function.