Gemma Scout is not

Dead, cloned, or comatose. She's fully alive.

It's become almost canon on this thread that she died or suffered some catastrophic injury and is either cloned or brain dead.

But I don't think this is the case. I think she's a permanent innie, as in never leaves Lumon. But she is physically alive and well.

We see her walking, talking, with no signs of physical injury.

When Cobel is spying on her and Mark's wellness sessions, Milchick remarks "it's good they don't recognise each other , it shows the procedure works"

'They...each other..' implies either one has the capacity to remember the other were it not for severance. That rules out cloning or brain death.

We don't even know if there was a car crash, or if there was, if she were even injured.

Mark never visits her grave. Maybe they think she was cremated.

My working theory is that Gemma posed some sort of danger to Lumon. They found a way to kidnap her by staging an accident, severed her against her will, and kept full time inside Lumon.

It's also possible that when she's not Ms. Casey, she's Gemma. But imprisoned.