All that happens is that they may have to pay more coins instead of less for the interest and capital release. They don't lose money as these coins are free to them and they have a large reserve (which they never even needed to use). The problem when the coin value doesn't rise enough (they can obviously adjust interest rates) is that it will cause inflation.
You're on the right track. When the price of their token starts going down, the company has to pay out more of the token to achieve the desired USD value. This causes the price to drop faster, which causes them to have to pay out even more of the token, and so on in a vicious circle until the token is worth very little and the company runs out of its reserves.
Your use of the term "inflation" is a little confusing, but I guess you're talking here about price inflation rather than monetary inflation. What you call "inflation" is presumably the same as what I mean when I say the price of their token falls.
It's not a problem if at times it isn't deflationary as they don't actually lose any profits. Do you understand now why it's a good model as it prevents the company from dumping the coins as if they did that it means they have to pay more coins for the same amount of daily interest?
Once the price enters its death spiral it will tend to stay in it until it hits the floor. That's why this isn't a good model. They're promising to generate steady USD returns while not having any source of income with which to actually back up that promise other than interest from new suckers buying in. The use of an intermediate token to obfuscate what is happening was clever, but doesn't change the fact that there's no real activity generating the promised returns. While the token price goes up they can pay their promised returns and when it falls they quickly find that they can't.
You make statements such as 'death spiral' as if you definitely know what was going on with bitconnect. The evidence was there to be seen. There was no death spiral, just they didn't want to get into legal issues. The day after the Cease and Desists they had some sign in question about where customers were from and blocked new loans for people in those states but allowed people to carry on receiving interest. They had told their promoters to stop promoting for weeks too before they closed the lending. However, did you see that their price was not going down? It was still near its recent $300 all time high and was even higher than this for a while (even the 14 day average was 20% higher).
Remember that this interest was easy for them to pay since most of the BCC in the lending was always locked up and the interest they did pay was far less than they could have paid. They used the massive profits to market the coin and even created lots of music videos to promote it.
Even if the price was falling (which it wasn't) it would never actually inflate the circulating supply for a long time as it took about 300 days for lenders to get their capital back and about 3 months even at 1% per day to even get back the same number of coins they put in lending (assuming the price didn't go up at all in those three months, which we all know it did). There was no real way the model could fail without people who didn't understand it complaining to authorities.
I just checked the graph again and it only reached $300 2 months before it closed and $200 was the all time high 3 months before it closed. It also had peaks of around $450 so was nowhere near any death spiral. Even when bitcoin fell from $20k to $12k in a few days around 18th December, BCC went from $450 to $220 but then went back to over $400 almost immediately despite bitcoin being worth around $15k (still a 25% fall for bitcoin but not BCC). Bitcoin then went from $15k to around $10k in the few days before bitconnect closed the lending, but the BCC coin was still in no trouble in the $200 to $300 range (which were recent all time highs only reached in the previous three months). Obviously the bad press wouldn't have helped but they were doing at least as well as bitcoin.