If they cut corners, the risk could go from a tiny possibility to an almost guaranteed disaster. I wonder, if you told the people paying such large dollar amounts that they might not be able to track the sub if it got lost, would they have stepped aboard?
Surely businesses providing such services have a duty of care to their customers? Ok, so you might be trying to provide an 'exciting' experience, but it can't really be much different in principle to an adventure holiday company, a theme park with 'thrill' rides, etc. The service you provide may have a certain level of risk, but if you know that there is a greater degree of risk which you as a provider could take reasonable steps to mitigate against (but you don't), then surely there is a basis for corporate negligence or manslaughter charges right there? Things like a secondary power and/or propulsion source, or a backup means of communicating with another vessel or the surface, should be the minimum safety for a deep-sea diving vessel such as this.
This reminds me of the horrific Kursk submarine disaster, but that was a slightly different situation as it was a military vessel and there were multiple faults and failings which led to all 118 crew dying, and the sub lying on the bottom for over a week before rescuers reached it.