For billionaires, making investment in bitcoins seems to be more correct. Even if they make some loss, it will not make much difference to their lifestyle.
I think different type of billionaires will approach this is different ways:
1) Someone who has become a millionaire only by his hard work and started from a very small capital will be very careful with any money he is spending no matter what is his current net value. Another thing we should not forget that such a person will already have a lot of successful business working for him which require continuous investments. He will always give preference to these while investing money in comparison to bitcoins.
2) Then we some people who inherited a lot of money. Such people may like to invest in risky things like bitcoins.