There are three major ways that reduced asset values have been dealt with by different countries:
1. Asset guarantees. This was used in the US for Citigroup and Bank Of America. This was done to make them more attractive for merger. This doesn't cost the government much initially, but future liability to the taxpayer is uncertain.
2. "Bad Banks" Used in a limited way in the US for Bear Sterns (that was allowed to go bnkrupt) and AIG (government became majority stockholder). Sharply reduced valued assets were removed from the balance sheets of these firms. Liability of taxpayers is not clear to me. This approach could be similar to removing the rule that non-performing loans are a charge againt a bank's capital ??(the method I have been advocating).
3. Public Asset Management Companies (AMCs) Distressed real estate related assets purchased by an AMC. (I am not clear about the public liability, but I suspect the government is left holding the bag.) Ireland used this method, buying $97 billion constituting 44 percent of GDP.