I'm sorry for the loss of that beautiful little one.
I wish it were not so, but there is always loss with getting these little guys to the customer. Whether the store is the one that takes receives the DOA or if it is the customer, it happens and we all wish that 100% of deliveries could be death and injury free. Heck, we can't even mass transport people 100% accident free. It just seems very personal when it happens to us.
I believe the seller did right by you as best he could. I know many of the sellers in their DOA policy require you to submit picture proof before opening the bag, and I see that this seller sent you a replacement at their expense with proof after the fish was in the tank. It might be just me, but given the protections sellers have, this one went above and beyond. I understand the reasoning for the seller policy, but I wish they all treated customers this way.
I know this doesn't help when you lose your dream fish but here's a little story about my Mishi (avatar pic). He wasn't what I was looking for when I bought him, I thought I might regret buying him when I brought him home and I questioned buying him when he was constantly sick. If you gave me a chance to do it over again, I would buy him again without hesitation and I wouldn't trade the time he spent with me for any other fish out there.