This does tally up with what I've been hearing. Where I'm at there's been a few hires straight into senior. I've not heard of an official junior freeze. At the same time it's been a long time since I've seen a new one.
The problem, as I commented prior, is that if we no longer bring in junior devs to gain this kind of experience, we lose the flow of junior -> senior. But in most places, the people making the decisions won't consider anything beyond the end of the current fin year.
I don't know if they have much of a case to sue you, if you fall through the cracks on their own negligence. Fire you, yes. Sue, I am doubtful most larger businesses would even try. They'd rather solve the problem and sweep it under the carpet in my experience. Not USA experience of course, but still the attitude would be similar I expect.
I would worry a bit about whether they're allowed to give negative references though. Because if so, it might not be so easy to get another job after.
Best move would be to line up another job to start like a month before the review, and never reach the review stage. Even if discovered, most people that would "know" wouldn't really be driven to report anything if they're leaving anyway. The "not my problem, and this will make it my problem" attitude in big companies is real.