With Wrike, an unassigned task will get lost in the 'cloud'. To prevent losing these tasks, I created a report at the root folder that sends me a daily report of all unassigned tasks. Has come in handy more than once. A way to help prevent unassigned tasks is to have folders automatically assign tasks based on workflow. My InBox automatically assigns to me, and even sends me a notice.
I hope this tip helps.
Update: The report option will not locate an unassigned task that has not been assigned to a folder. Those tasks head to the root directory. Unfortunately at this time, including the root folder, is not an option. Until it is, be sure to click on the root folder once in awhile to look for unassigned/not in a folder tasks.