What happens to deleted tasks in todoist? Is there a way to have deleted tasks sent to a folder or something?
Deleted tasks are literally being deleted with no way of restoring them. Only right after the deletion, you can use the "Undo" option at the bottom, but once it's gone, you can't recover them.
That said, if you prefer to keep this data, instead of deleting these tasks, you could try to group them into one project and then archive this project (it's a Premium feature, though).