"In case????!!!!"
Strongly suggest you ask your 'computer center' to clone your instance of moodle to a development instance (a copy of). You can then 'play' all you like with the development instance to see what happens and how to do such things as restoring a deleted assignment work or don't work.
Recyclebin was created for 'boo-boo's'. A Teacher or Site Admin does have to step through at least 2 steps to delete giving them time to consider if what they are doing is desired. 'Thimk before you click!'.
In the event user deleted anyway ... one can restore IF ... IF ... a course backup was made ... catch 22 - how old is the course backup?
In the restore process step through each screen. When getting to the screen that list all modules in the course, deselect all but the assignment that was deleted and restore just that module. It will not come into the course in it's former place ... look at the bottom and move into position desired. Check completion tracking if you have that turned on for that course.
Again ... 'catch 22' is in play ... if the backup was from 4 weeks ago, restore will restore that assignment as it was 4 weeks ago. Some students who may have completed it, will be surprised they must do it again - can't be avoided.
Again ... Strongly suggest you ask your 'computer center' to clone your instance of moodle to a development instance (a copy of) so you can try out those 'in case' senarios.
'SoS', Ken
by Ken Task.