It is not a matter of just being shut down due to low volume. The rates that you get depend on the volume. So the "back up" gateways end up so expensive you have no interest in even keeping them around.

From my experience you end up being tied pretty hard to pretty one provider and as long as you make fraud prevention yourself you can stay in business. Problem is that if you do all the fraud prevention stuff yourself then why do you need braintree for? To just invoke a .charge(100, "EUR")??