"Death" before The Second Dream

[Date_Terumune]

I bet you seen Matrix movie...

 

I think it works the same way.

[Necromanrius]

Since we use Mirage as an example. That Frame, without energy and her shields down, tanked attacks from Sentient ships and ripped those drones with her bare hands. Nothing at all like the glass cannon we use now.
 But her death was permanent.

Also, we do not know if Tenno could switch Warframes before. We know they can do it now. Maybe before Transference was much stronger, but forced you to stick to one Frame and you died if said Frame died, but it got a massive boost compared to our current models. My theory, Transference was changed. By the Lotus herself. She has the motivation, she wants to protect us. She freaking hid the entire Moon in the void just to keep us safe. A nerf in power in exchange for immunity to death? you'd bet she'll have made the decision faster than a Loki can Switch!

[Littlerift]

We don't actually know if the Operator controlling Mirage and Limbo died, we just know that the Warframes were destroyed. However, Lotus does appear sad about Mirage's death, which rather implies that Lotus feared that the Operator had died and not just the Warframe.