Honestly, I think there is nothing that can be done now. He owns the place and it will only get worse. I know it sucks as twitter was a great resource for many people but those days are gone forever.
He has such an inflated ego I believe he would rather burn it to the ground than cut his losses, sell it and move on.
He already reached the 'blame it on other people' stage, at least. That's how people like him conserve their ego while admitting defeat: "someone else did this to me".
A petition to remove Elon from Twitter is not like that. It's an important petition to save the world's most useful social networking service. Also, you should stop thinking that Change.org is a bad website (while we see some stupid nonsense petitions).
But he still owns it and has control over the company as chairman and has made many bad changes to Twitter. Maybe the petition should be repurposed to remove him from Twitter completely.
How is a petition going to make him sell his controlling stake in a private company? He's going to see the petition and say, "well, guess I better sell Twitter."