Most countries will not accept Bitcoin as a proof of funds neither will my country because they still think Bitcoin is not to be taken seriously as a currency or asset. Bitcoin is volatile and the price of your investments can reduced or increased  depending on when it gets viewed therefore they will want a fiats statement of account. Better your friend just sell some Bitcoin and have fiats that he will use for the verification and go on his business trips. We should not be having our money in just one thing because we do not know what tomorrow holds. Betting on Bitcoin is a good move but we still need fiats for some important things like proof of funds, therefore we should also have emergency money in our accounts that can be used for this type of verification and for other things that might come up.