Just to take a quick alternate view on informing the company about the problem.... why?
Why spend more hours giving this info to managers who are currently not prepared to know or understand the current organisation, culture and situation?
Why take this time to guide a company you no longer work for to develop and improve them?
Why help your likely future opposition?
The one positive from doing it is that it is cathartic, you get it out of your head and perhaps you feel like you have accomplished something, but the physical result would be minimal. Harder yet is not being personally critical of those people and situations in the future, so it's something you can learn from, understand and see the signs earlier next time but unless you are there as the business consultant and restructuring 'head hunter' then it's actually not so much your responsibility to fix and even less your place to tell 'all knowing' managers what they are doing wrong.
Don't burn your bridges, just leave with a smile and move on happier elsewhere.