Here is mike's response to me via email:
I ship only using fully trackable shipping and will avoid funding if the carrier will tell me in writing they lost it. This applies only to coins I send out, not ones remailed by resellers.
Looks like I'm doing the exact same thing. Coins may exist unfunded if they are reported by the carrier as lost during shipment from mike to the original buyer and in no other circumstances. In a similar circumstance I would be doing the same as it makes the most sense.
If Mike chooses he can verify this quote as I have copy-pasted it here.
Keep in mind that this scenario has not happened for me. So my method of funding will remain until I can see a better way to go about dealing with a situation like this. Given ALL of my packages are going through USPS registered mail, it may be some time until I see this manifest itself.
If a package ever went missing or stolen through the carrier and I got confirmation (in writing as well) I would eat the cost and replace the package to the buyer.