If you delete a user in Kintone Users & System Administration, data associated with that user is also deleted.
You cannot undo delete or restore the deleted user or its data.

If you want to temporarily forbid a user to access Kintone due to leave of absence, temporary assignment, or other reasons, we recommend you to deactivate the user instead of deleting the user.
Deactivated users cannot log in to Kintone.
Deactivating Users