The accounting of "cryptocurrency" is still being developed, but, yes, Bitcoin holdings take an impairment when their value drops below a certain point. This doesn't typically affect cost basis. It may be deducted as losses on a tax return but that might impact cost basis. I've heard from other accountants (a year or so ago, so take this with a lump of salt) that some companies are trying to account for cryptocurrency as inventory, as a "hot asset," as cash equivalents, or as intangibles.