Depends on your perspective. Prices dropped significantly because people started to prefer dollars to some extent. Several of the large exchanges that existed back then are still around, however, and others were acquired. Examples of those still around: Coinbase, Bitstamp, Bitfinex, Kraken. Sure I'm missing others.

I mention the above only to say it didn't feel like a true bank run to me at the time. People were still able to get in and out, but prices were certainly depressed. And several of the exchanges survived.

there was a huge spread between the price of bitcoin on the exchanges.

i also distinctly remember people sending money to mt gox LONG after every mention of them on the internet was followed by angry people calling them a scam.

Today's ecosystem is different in many ways. The next big exchange failure, especially it one in the US, will have a cascading effect.

hacked != failed

> as long as their books balance

This is a really strong assumption that I wouldn't bet on.

I'd also be worried that any exchange that used tether, would realize their jig is up, and just run away with all the coin.