Since there's a limit on Shizus life span, I'm surprised that one of the gigantic darks primary objectives wasn't to find someway to extend her life, like taking a proper crystal from a proper zoalord. Although this probably wouldn't work, as there would then be a risk of her being subjected to Archanfels will, but then Guyot did alright for independence!

It may not of been a high priority for Agito. At least not yet, hopefully he got a change of heart.

He can possibly revive her again later with a new Zoa-Crystal. It's been done before, so even if she expires, there is that option. I suspect it to be fairly traumatic and there might be a limit as to how many times that body can handle a reprocessing for a new crystal.