Why isn't Y'shtola dead?

I don't understand the lore that well, but surely she should have died or become some form of aether/energy substance instead?

She teleported herself into the lifestream, which isn't that part of the planet? She can't just come back unharmed? That's plot armor.

She should be space goop.

How exactly did we manage to pull her out of a tree?

She didn't come back unharmed, she came back blind. And Thancred came back unable to manipulate aether.

We got her out with some serious help, including from the Padjali who commune with the planet, and Y'shtola's sister. It wasn't exactly an easy achievement to fish her out.

Um.. Because.

Why isn't poster girl dead?

I wonder

Entering the Lifestream is actually how all teleportation works. The difference in what Y'shtola did was that she teleported without an attuned aetheryte to act as a beacon, which has a high risk of leaving the caster adrift. Eventually she would have broken down completely but we managed to fish her out quickly enough that she only lost her eyesight.

As for how we got her out we got lucky there, she ended up in the Twelveswood, where a combination of her sister being present (with her similar aetheric makeup helping to pinpoint Y'shtola within the lifestream) and the Elementals being convinced to help. Without that she'd have just stayed stuck in the Lifestream indefintiely until her aether fully dissipated.

she is untouchable.