Something like 80% of trades on the market currently involve tether, and tether accounts for ~$3 billion of (presumed) cash-like holdings. If it collapses then liquidity of the market is going to be severely hit, and the people trying to exit to fiat are likely to cause a variety of bank-run type situations.

These will be exacerbated by exchanges which have been run in bad faith and which do not have either the cryptocurrency or fiat reserves they claim (see Quadriga CX for a recent example).

Either way, it's going to be interesting to watch.