Question About Taric's W: Bastion

I was playing ARAM against a Taric, and other champions obviously.

So Taric has Bastion on an ally, and he begins casting his Ultimate. Before the Ultimate is cast, we manage to kill Taric. However, his Ult still cast from the Bastion ally.

The mechanic of Bastion allows Taric's spells to be cast from the affected ally. However, considering it's not actually the ally casting the spell- I think Taric's death should cancel the spells being cast. Specifically his E and R- the two spells that Taric can cast and die before the spell is actually cast.

Bastion is Taric's ability, I imagine it works like a mirror. So if anything happens to Taric that would cancel the ability being cast, the same should apply to his ally affected by Bastion.

My question: Is Taric's Bastion meant to cast abilities despite Taric's inability to do so himself?

Honestly, I'm not complaining. I'm juts now learning it works this way. I can adapt. I just don't think it makes sense- because Taric is the actual source of this magic.. you know?

(Still mourning the death of OG Taric) R.I.P. Imbue and Radiance