Only archived tasks can be deleted.

See: How to archive a task?

Notifications

No notifications are sent to task watchers that has has been deleted. Only a mention about it in the Primary Message Channel can be ephemerally visible.

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Who can delete tasks?

Only an assignee, or a task creator, can delete a task.

How to retrieve deleted tasks?

It’s impossible. Tasks are deleted from the database and it’s not possible to retrieve them.