The advice is simple with only four words: don't give in!
What's more, freezing three feet is not a day's cold, where there is any click, it is a cumulative quantitative change, will form a qualitative change, compared to the reason for his resignation, your more important focus is: the opportunity is coming.Don't bother to think about it, whether the office politics is on the wrong side, whether it is corrupt and bribery that has been captured, whether the competitors have dug the wall... Your imagination of being afraid of repeating the mistakes of the past will become an obstacle to your courage to move forward!
Since the boss asked you to replace, it means that you are the best choice in the team at present, which is your recognition.
Do you want to say to the boss "Boss, do you think I can do it, in fact, you are wrong, I am not"?
You've drunk a lot...