I think big CDs should never ever be RNG. You pop them when things go south or difficult phases are coming and you need them to be reliable above all else. Flat heal increase, dmg reduce etc. but not a chance for something.
RNG is something you can add to frequently used skills without cd to add a nice bonus without making the proc mandatory.
Some guaranteed life saver would be nice though.
Keeping freshly raised people from instantly biting the dust again or saving the raid from being grilled by raid wide dmg if the healers couldn't keep up. I'm always a bit reluctant about skills that enable you to ignore mechanics because it usually leads to classes being mandatory simply for one or two skills. So it should come at a really high cost to have you own personal LB.
And maybe not as a rework of Asylum but as a seperate skill. I still think Asylum could need some work, it feels rather boring right now.