Hi,this is my advise:
if a task want to suicide(delete itself), the opration can diliver to the daemon task( timer task) with a timer pend call, and daemon task should be give a very high priority, so it can do the deletion right away,and then asign NULL to handle of the task to be delete after the delete in the daemon task.
then you can check at other place whether a task exist by checking the value of its handle, be NULL or not.