In the case of SBD there is no forced liquidation. The only thing that is changed is that manual conversions will not give 1$ of steem anymore, but less. The conversion amount is computed such that when all sbd would be computed at once the converted steem is no more than 10% of the steem in circulation.

The markets are quite rational and the price you see on coinmarketcap is usually close to the amount guaranteed by conversions.

I have made a lot of posts about this:

overview and pre HF20 prediction
simple computations
full computation
last update