I have had fish delayed in shipping an survive. Most recently this spring. I sent 19 0r 20 juvenile plecos via Priority mail. They were going a 4 hour drive so I only used a 60 hour heat pack. The post office misplaced the box and it arrived 8 days later. All the fish were alive when the bags were opened, but a number died in the next 48 hours. however in the end at least 2/3 recovered and now live in new homes.
It all boils down to how well fish, snails or shrimp are packed as to how long they can last. it also depends on the fish.
I would suggest you email the sender one more time. Tell them they should have known better than to ship without confirming their buyer would be there to receive the shipment, especially after all the delays. Tell them unless they respond right away that, to protect yourself, you will refuse delivery and that you expect a full refund. Further, you need to know that if you do accept delivery the seller is prepared to hear that all the contents are DOA and would have to replace them, at their own expense or issue a full refund, including shipping.