Good point. This is one reason why cloud mining is the perfect medium for ponzi's. The question that one has though is are the affiliates and interest in mining enough to sustain the higher payout for a flat or decrease in difficulty? I believe that some of these operations will be forced to shutdown because they cannot attract enough contracts from new and existing clients to fulfill their past contracts. There is a limited supply of people interested in mining and a large amount of options so this may prove fatal to them.
There are two kinds of 'forced shutdown' points; there is the point where the ponzi or fractional reserve mining operations actually runs out of money and is forced to close. But (long) before that, is the point where new sales < dividend payouts, and a ponzi operator would benefit from stopping right there and running away with his maximized loot.
The first point, it may take a very long time for most ponzi's, and potentially never for some that sold at high prices, and/or if difficulty growth picks up again with the next generation miners.
The second point, applicable especially to all the anonymous ponzi's, we will see many of them run off in the coming weeks and months, but thats gonna happen regardless of what difficulty does IMO
It is trivial to securely prove they have the hashing power to sustain their clients contracts even without any effort or audits. I suspect the reason they don't do this is because all cloud mining schemes at minimum partially oversell their hash rates.
I wish it was that simple, but its not. In fact its trivially easy for a scam operation to 'prove' hashrate it doesnt have. They can just rent it from nicehash for the duration of the scam. That would reduce their profits, but not to the point of being unprofitable since they would rent only for a few weeks or months, but sell contracts for x years. So be careful accepting blockchain proof of hashrate alone as sufficient. Instead, I tried listing 7 criteria and applying them to most companies in the link in my sig. Its not waterproof either, but complying with most or all of those criteria is certainly a significant burden for a scammer to overcome.