While I agree that the impact on current reservation holders would be negligible - for the sake of discussion, put yourself in Tesla's place.
Production has started, is rolling along. Someone has totaled their Model S and wants to go to the front of the line. Let's say there are 9000 people currently in the queue, reservation numbers in hand - and the owner of the totaled Model S shows up. While 8999 of the people currently in the queue think it's no big deal, do you (as Tesla) really want to deal with the guy who is freaking out because he paid for his spot in line and by god, you'd better not bump him even one spot to accommodate someone else?
So while I assume there are some empty slots in the queue & Tesla will help where they can - the paperwork involved and potential for a lawsuit/bad publicity ("entitled Signature holder who wrecked their S forces everyone else to wait, again") just wouldn't be worth making this a policy.
Again, I'm sure there are going to be gaps in the sequence where they could take care of this infrequent/unlikely situation without impacting everyone else. But while yes, 'we are a family', for business reasons it would be foolish. More than foolish. And as a stockholder, I'd prefer they not invite a lawsuit. And give the next unspoken for slot to the person who lost their car. Which may be no wait at all.