Depending on internal policy, this could be reason enough for the employee to be fired.

Unless explicitly authorised, I’m not allowed to quote an internal email on a public forum.

As I read it, it looks like it was decided, by IBM, the employee would no longer be a maintainer and adding a personal email to the list of maintainers was a misrepresentation of their current role.

I suspect that HR is probably discussing termination procedure as we speak and this will proceed unless the PR pressure is overwhelming and makes it difficult to retaliate.

Unlikely since termination would mean that Lijun can resume work on the kernel.

That might depend on non-competes (legal in most states outside California), and how they're interpreted.

IBM's bad-will generation here is large.

Maybe, but he still won't be paid for it.