You can't claim the tax loss until the administrators issue a...

You can't claim the tax loss until the administrators issue a letter stating that the shares are worthless. If BNB drags this out, it could take up to 2 years to get such a letter.

Since it looks like the shareholders will get nothing now, the best thing that could happen is for BNB to go into administration, so that the administrators can legally say shareholders have no value left.