Do you have an agreed date of separation (or date of valuation)? If so, why would you not use the value on that date when calculating equalization? The only exceptions I could think of would be if the value on the date of separation was unusually high (maybe this is a seasonal business or one which is subject to boom-and-bust cycles?), and the current, lower, value of the asset is more typical of its actual value over a span of years; or if something disastrous happened that was completely unpredictable and outside the control of either party (e.g. a meteor hit the business the day after the insurance lapsed).
If the loss of value of the asset means that one party (presumably the one that has the asset now) won't have the cash to meet the equalization payment, perhaps the two parties can work something out whereby non-cash resources like pension credits are transferred instead, or paid out over a long period of time, kind of like equalization on the installment plan.