However, there is still the situation where some BitAsset holdouts refuse to sell (potentially lost their keys) which means that there are some Shorts that are unable to buy and then cover to free their collateral.
This is an extreme case, which would hardly happen.
It's not a good idea to touch users asset, because someone might have reason to hold bitasset on hand, instead of put them in the market.
If the bitAsset in the market is insufficient for the shorts to cover, that means the market needs more bitasset, then people will issue more by new shorts.