User blog comment:IamJakuhoRaikoben/Chapter 386: Galaxia Blade, Review./@comment-24066070-20140531164902

I must say I'm quite pleased to see the CSK's power to be directly related to Lucy's stamina.

This means he's not some Deus Ex Machina who will instantly turn the tide of battle in Lucy's favour and that Lucy isn't invincible the moment the CSK appears, thus still maintaining the fact that the biggest threat for a CSW is the fact that he/she can be taken out before the Spirits win the battle.

As for Marde's petrification, my bet is that the CSK transferred the effects of Alegria from the FT members onto Marde.

I doubt he'll be gone for good, since it seems the other Demons don't know how to actually revive END (at least that's what he hinted during his conversation with Kyouka)