Let's pare the situation down to a minimum.
The bankers involved decide to invest their companies money in assets. These assets are valued periodically. If the assessed value is greater than that originally paid by the bank, a gain on paper has occurred, Bonuses have traditionally been assessed on the paper gain.
But the gain is only on paper- the real gain only occurs when the asset is sold.
If value of the asset falls, the gain can turn into a loss. But the bonus has long since been paid to the individual.
The losers are the owners (shareholders) of the bank, whose investment declines sharply. The losers MAY also be any new investors (aka Government using taxpayers' money) who take a stake in the bank by injecting new capital into it. But those new investors may also take a handsome gain if the value of the bank (reflected in its share price) rises.