The result is if the majority of nodes run a common set of code, that code becomes the specification even if the code deviates from the spec. The majority will follow that deviation, because it is the code they are running. If you think about it, that is exactly what a hard fork is. A hard fork is a majority of nodes agreeing to deviate from the existing specification. This holds true whether the hard fork was intentional or if the hard fork was unintentional (due to a bug).
if the code is the specification then the code can't deviate from the specification. What happens if the code fails to converge to consensus is that the specification/code is proven to be broken, in which case the majority is forced to accept a change to the specification if they want to have a consensus system. In other hard-fork cases the majority may choose to accept a change, but it isn't forced.
Agree with Justus about multiple implementations.