`else` would work fine here, since `None` and `not None` are entirely complementary.  :)  But the command to update the group is exactly the same - there is only the additional `self.resources.add(...)` if dont_delete is not None.  Maybe just:

if servers_on_group.desiredCapacity != 0:
    self.autoscale_client.update_group_config(
        group_id=group.id,
        name="delete_me_please",
        cooldown=0,
        min_entities=0,
        max_entities=0,
        metadata={})

    if dont_delete is None:
        self.resources.add(group.id,
                           self.autoscale_client.delete_scaling_group)

Would simplify it?  I think that covers the three cases here, but please make sure I didn't mess that up :D