You had data backups, right?

The middle road would be not firing him but not saving his spot and hours if you find a more reliable performer. There are a lot of layoffs right now and probably plenty of people who would be happy to have a decent job depending on the specifics of your company. It isn’t personal. You just need somebody that is reliable and available to get the work done on time. That isn’t really about you or about him but about keeping your team and company successful so you don’t succumb to the same economic problems all of us are coping with right now.

Don’t send anything until overdue balances are sorted first.

If you mark all the trash as spam Google will learn to get rid of it for you pretty quickly.

Frequently, even if you have hostile terms and conditions labeling yourself as not responsible for shipment loss, you actually still are responsible for ensuring the customer receives the goods even if the a hippie company screws up. Particularly under credit card processing agreements. You might benefit from a tool like PirateShip where insurance comes from a private provider with much friendlier pricing than you get from the shipping firms themselves.

Filing a postal claim on an uninsured package does nothing generally speaking. What to do depends on your ethics and the value of this client and the cost of properly insuring future large shipments and what you envision the future of your firm to be.

Many people track the contact info and addresses of lost shipments so they can deny / ban a client that has too many or look for weird patterns.

It depends partly on how you want the business to go and and partly on how it actually goes. You can convert into a C corporation, where you have more control over how much comes in to you as income or dividends, and how much is kept in the business as retained earnings or R&D investment funds or internal asset management accounts and the like.

Definitely get a solid bookkeeper or accountant with appropriate experience to guide you here. This is a touchy situation that needs more than just Internet advice.