While what you say is true, keep in mind that those small exchanges will not even account for 50% of the orders.
In such hypothetical scenario I can guarantee that small exchanges will not take that risk (or they do it but they
won't be able to sustain the demand).
It happened, but for NANO (formerly XRB). When Mercatox had issues handling the transactions, Bitgrail was next to open its doors. That caused a soar in its prices.