Assuming they were using threshold cryptography, they could have easily configured some redundancy into the system, e.g. by requiring 3 out of 5 people to decrypt it instead of 3 of 3.
It's easy to blame the one guy for losing the key, but he could have gotten hit by a bus or lost the hard drive in a house fire and they would have been equally as screwed. This is more of a system design failure than a PEBKAC failure.