Maybe we should seperate between cash money and money at the bank account.
Cash can be taken by your opponent when you lose a cock fight (the amount depends on the ratio of money between you and your opponent), but except you have really low cash (under 5k, which is the minimum), you won't lose everything. Furthermore you pay for getting out of jail/hospital (like mentioned below), but not ALL your money .
(Just in case you are a member of a gang. If you 'lose' money from your safe bank account, you should be sure nobody, you gave your password, has spend it to your gang. This can be seen at the gang HQ under weekly achievements or at the general gang overview for the whole time.)