The tl;dr here is simple. If you live in a "at will" state, you can be terminated for anything if the reason is not based on a [protected class](https://www.eeoc.gov/employers/small-business/3-who-protected-employment-discrimination). Find a new job as soon as possible (especially because of your actions).

The longer answer sucks, but I'm going to dive in to it anyways:
* You weren't unofficially demoted, you were reorganized. Things aren't consistent in a hierarchy between organizations. It sucks, but you were left wherever you were.
* Unpaid overtime is wage theft. It's one of the biggest problems facing labour in the US, and [is bigger than all other theft][1]. It's insidious because workers will allow it because they believe it will bring them personal gain in the form of advancement, or preferential treatment. Look at one of the people that was promoted.
* You took a month off. Management in a company like yours will _never_ understand that, and you are a _further risk_ of long periods of time off.
* Whatever reasons that project failed, you were at the helm in the end. That's the definition of a [fall guy][2]. If you managed to pull it off, decisive victory for your supervisor. You didn't, decisive loss for you. Made worse by you do doing it all the while saying it was going to fail.
* 40h of unpaid overtime? You're not in a position to be rewarded for it, and you donated 25% more of your time to an employer.
* Promises to promote fast, or "grooming", or whatever are carrots on a string to get that sweet 25% more of your time. You'll know you're being groomed without being told because you'll be present when you shouldn't be, consulted when you shouldn't be, and given perks that you shouldn't be. Don't buy in to the myth.
* You're probably seen as a risk because of your actions with the emails. They may be breaking laws (highly dependent on where you work), and that makes it worse for you. Get out.


  [1]: https://digitalcommons.law.yale.edu/cgi/viewcontent.cgi?article=1731&context=ylpr
  [2]: https://dictionary.cambridge.org/dictionary/english/fall-guy