Two scenarios where this breaks:

* parent process is killed after it forks, but before it calls `waitpid`. Nothing even attempts to kill&wait for the child

* parent process is killed after it issues `waitpid` syscall. The child continues to happily execute while the parent is dead.

- waitpid returns after timeout, assume the process is dead, collect all zombie processes just in case.

- yeah this one is a bummer, write the child pids, collect them via a watchdog process