The cabal high command will notice that their Valus' keep dying. They will likely send a huge fleet to try and eliminate the guardians. The vanguard fears the cabal, did you know that? They know that the cabal we've seen are likely just a forward scouting group, sent to soften us up for a major assault. I doubt they will send the cabal emperor, but In forge of gods, we'll probably face a highly skilled general or commander. Note also that the cabal have been known to destroy entire planets. Maybe that will be the big threat in the dlc. We'll have to stop them before they annihilate us and the traveler. The raid, like before, will probably be our finishing blow to the cabal. We still have a vex dlc though, so it's probably best not to speculate too much. Whatever it is, it's probably going to be a massive pain in the ass.