Ryzom

What happens if you have a faction vs faction event and one side overwhelmingly outmatches the other side, e.g. 50 Karavan show up and 5 Kami?
Will there be a mechanism to rebalance the two sides?

There shouldn't be. If someone chooses to be on the Kami side by working on their Kami fame, they should NOT get "rebalanced" onto the Karavan side against their will. Or vice versa. That would render the entire point of faction PvP moot. If the Karavan side, for example, is outnumbered by the Kami side, that's their fault because the Karavan players weren't paying attention to event announcements/didn't feel like PvPing/etc..