Hi @louiscrush,
@MFrankJohnson is correct that there is no way to “undo” deleting a user.
The leads who were associated with that user won’t be deleted, however, their owner will change to “deactivated user” (see screenshot).
If you did want to sort by the owner and reassign the contacts after you’ve deleted the user, you can add the user back (using the same email address) and the contacts will reassociate with their owner automatically. Then, once they are reassigned you can delete the user.
Thanks,
Jenny