Don't burn your bridges (behind you).

proverb Do not act in a manner that causes irreparable harm to your past relationships or connections, as you may need them later in life. He had outstanding debts with pretty much everyone in town before he ran away, so no one around here will work with him now that he's come crawling back. And that's exactly why you don't burn your bridges. I know you're angry with your employer, but you've got to quit in a tactful, professional way, in case you need a reference from them down the line or something. Don't burn your bridges behind you. Why would someone announce they were quitting and also proceed to insult the boss in front of the whole staff? Like, don't burn your bridges behind you—sheesh!