"If we were to do this" = an unlikely (but still technically possible) situation. "All hell will break loose" = chaos!! Technically, the writer should have used "would" to be consistent with "if we were", but this is one example where "will" (highly likely) is used instead to dramatise the possibility. One more thing: a verb can ONLY be in the base form when it follows a modal. "Could anyone explain the following sentence?" You don't conjugate "explain".

The devils will be unleashed, as a consequence; I don't know anything about your friends, I just hope it is a metaphor.

That means that if they did that, they would cause serious trouble afterwards.