They knew it would be the end for them ...at least for who they once were, but it was the only way.

It wasn't the only way ...because Sul was only pseudo supreme.  The truly Supreme only wanted to see if the others would sacrifice their very existence for the higher purpose.  The Sul group had literally done that also, but it was a matter of seeking ConSul, being "conned" into believing that which was not higher ...sacrificing for their own unknown inevitable loss.