Strictly speaking, yes, you can kill a Fog Bank through combat damage. I can think of 2 general ways:
(1) Remove Fog Bank's ability (the one that prevents combat damage). An example would be if you resolved the spell Turn to Frog before combat damage. Without the relevant ability, combat damage to Fog Bank would no longer be prevented.
(2) Use an effect that does not allow combat damage to be prevented. For example, if you resolved the spell Skullcrack before combat damage or if Fog Bank were blocking a creature whose damage can't be prevented, such as Malignus, then the damage would NOT be prevented. This interaction is governed by the following rule:
101.2. When a rule or effect allows or directs something to happen, and another effect states that it can't happen, the "can't" effect takes precedence.
In this case, Fog Bank says "prevent combat damage" and another effect says "damage can't be prevented", and so the "can't" effect will win out and Fog Bank will not be able to prevent damage.