A company doesn't have to be engaged in a scam to be liable for damages. Savings losses are damages to be considered and will have to be covered by the balance sheet of the supplier if they don't live up to their oral or written promises. The only thing which you can say goodbye to is the potential profit derived from the purchase or costs for legal action.
Should the TOS conflict with those oral or written promises a judge will have to determine whether the particular terms would have had to be actively advertised by the supplier, i.e. making them initial off them individually. Also what needs to be determined is whether the promise was an attempt to mislead the customer - which goes into the direction of consumer protection - because consumer can't be expected to study TOS or consult a lawyer every time they make a purchase.
I'm not saying there isn't an argument for not meeting expectations and there seem to be plenty of people poring over whether or not specific statements of what we should expect are enforceable. I'm just saying being disappointed because you didn't receive what you expected is not the same as being scammed.
I think HashFast can wiggle out of the entire ROI argument by saying that they had a rosier prediction of the future difficulty than reality. In fact, if difficulty just stopped dead in its tracks between now and batch 1 delivery + 90 days, then everyone here would get their BTC back, as unrealistic as that sounds, it's "possible". I know nothing about legal matters, but it seems like if the possibility, as remote as it may be, still exists for customers to have the promises fulfilled, as long as they deliver the miners at some point and have enough "well, we can't predict the difficulty" language, then they're in the clear.
As for the refund in BTC/USD, I wonder if there's a precedent for someone paying for services in something like gold, the market changing, and then being paid back in not gold and that being unacceptable. That would be interesting if someone could find a helpful case of something like that.
My 2 cents: of the available options, the one that leaves me least out of pocket is getting the miner at some point and having a shot of getting my initial BTC back. A refund in USD is not acceptable, a settlement will end up in probably an unfavorable BTC/USD ratio and chance of losing even more money with no recompense. I feel dirty trashing HF on the forums because that is just pissing on my investment. I'm just a bit flabbergasted that they do not have enough sense to make some kind of attempt to communicate with their customers.