It is really only the perceived value which matters to a business - that's the value at which you can sell or replace your asset on the market. Offers above that price, you sell (and replace if needed). Offers below that price, you don't.

If it costs more to produce (and sell) the asset than you can sell it for, you're losing money and assets go down. If it costs the same, then in this example the net change in S&P assets would be zero.