usdt is not an investment vehicle. you don't "invest" in usdt. it's impossible for usdt to collapse unless the exchanges (or usd itself) collapses in which usdt is no more riskier than any other coins.
even if the so called scandal is true, and there isn't actually a single dollar in the bank, the value of usdt to usd will remain unaffected.
You can trade USDT/USD on Kraken, thus, yes of course it can collapse. Just this night it lost 5%.
..which doesn't mean there is anything wrong happening with it.. YET. Indeed, you can trade normal USD/EUR on Bitstamp, and it's not uncommon to see a gap of a few % between the pair on Bitstamp, and the "real" USD/EUR value. Hell, EUR even peaked at 1.4 USD for a brief moment on Bitstamp, probably because a whale made a mistake.
Still, the more you read about what's happening around USDT, the more you understand it's probably a scam. Seems to be all red flags.
Bitfinex isn't a small exchange, and some other big exchanges support USDT, I don't know when we will know the outcome of this, but it will be either really good or really bad.