I would like to think that Galio is a different circumstance in regards to how his petricite body operates with magic. Whereas normally crafted petricite is like a water balloon that can only hold so much water before it bursts, I believe Galio is like a car - you pour the gas in, and he uses it, allowing him to constantly be able to process the magic being absorbed by his body. I think this is the wonder that is Durand - his craftsmanship and skill with understanding how petricite works allows him to have created a perpetual machine of sorts that consumes magic as it absorbs it, thus never crumbling or breaking in the process. But since he was the only one who knew about this special process of crafting petricite, and he's now dead, the only crafters of petricite items these days make it in the flawed manner that can't process the magic as it soaks it.
So that said, Sylas would probably end up losing his cuffs in the fight with Xerath in the lore (or Syndra for that matter), as his cuffs aren't creations of Durand that were made with the magical processing capabilities. But even though Sylas has figured out to an extent how Durand was able to give it the magic processing capability and force the petricite to expel it's stored magic, it's still a process he has to manage, and I think someone like Xerath or Syndra would overload his cuffs before he could expel them. As for Galio, well, they'd keep him alive and kicking, which if I were him, I'd not want to kill them, but instead make them his companions who he can siphon life off of to be animated as long as he can.
