end of an expression?

This came up in conversation with my brother last night - amusingly, in a conversation about the joys of our current economy:

If the expression "bank on it" means to 'trust in / count on something completely, as you would a bank with your money,' then haven't we witnessed the end of an expression?

bank on something

Fig. to be so sure of something that one can trust it as one might trust a bank with one's money. I will be there on time. You can bank on it. I need a promise of your help. I hope I can bank on it.