I'm not really sure if that really achieves anything, though. If one of the Scions takes it on themselves to solo pull Zenos, well, that's probably on them. I think that if you wanted to do this, you're better off having Fourchenault pull a Teledji style coup and tie him and Sharlayan to the Lambs of Dalamud or some such. I think that the most impactful deaths are the ones that, in theory and in hindsight, we could have prevented. It's that Gwen Stacy effect.

Otherwise, you're just putting a developed character with potential on the bus for no real gain. Think back to your reactions from earlier in the game. There have been a few important character deaths to this point, but there's really one major one that everyone remembers.

A three boss council fight is easily doable, although adding a third tank is not really practical from a queuing perspective. You either need a boss that 'tags in' for one of the other two at set intervals, or is AI controlled rather than actively tanked (although tanks had have relatively little real control over boss movement anyways in these last two expansions).