Even if Legion-7's willingness to commit suicide is not enough to bring all of them and their tenth clone down, it is bound to work if they employ the assistance of the void universe in it too. After all, no world god can overpower the void universe.
What the void universe hates the most is tampering with time, so if they try to rewind time, the backlash should be heavy enough to kill them. Even if the First Sage succeeds against all odds and blocks that backlash on their behalf, they will be able to actually return to the past and undo what the First Sage did to them.
If that still doesn't work, then they will let CARNAGE lose or make Aeternus descend into his Demonic Spark. These are extreme measures that they don't want to do, which is why they are saving them for last.
It is a series of plans that cannot fail. All of Legion were of one mind in that regard. If they all fail, then they truly deserve to become enslaved by the first sage.
