What if a merchant prices their goods in fiat (like everyone), if they the handling fee in BTC and the BTC price has dropped 20% they've lost out. Bob has to send the goods without actually receiving the payment?
Maybe I'm not explaining it correctly but how can Escrow function well if the funds are sitting there in BTC for an extended period of time, no merchant will use that.
If you are doing multisig escrow the contract is with BTC and not Fiat. The amount of BTC cannot lose 20%. If it has lost 20% in USD it may have gained 10% in value against gold or the Argentinian peso.... the value of Bitcoin to other things is all relative.
Additionally, I think people overly emphasize the volatility of Bitcoin. People may assume they lost purchasing power in BTC with a transaction when they could have bought BTC for less independently but that is all hindsight bias. No one has a crystal ball and knows exactly when to buy so if BTC loses 10-20% in purchasing power for a week than recovers and gains 10-20% in value than what is the big deal.
All this means is you should diversify your assets and never use your BTC when it has less purchasing power when you acquired or purchased it.