Before leaving Twitter, consider archiving your Tweets on the Internet Archive's Wayback Machine. https://help.archive.org/help/how-to-archive-your-tweets-with-the-wayback-machine/
How to archive your Tweets with the Wayback Machine – Internet Archive Help Center

How to download your Twitter archive and Tweets | Twitter Help

It's easy to download your Twitter archive from your first Tweet to your last. Here's how.

@Geri Fairly sure you have to do that in any case...

@dangillmor I believe you can just leave, delete account, without making a backup.

I have deleted all my tweets but left my account live to prevent someone impersonating me.

@Geri Keeping the account for that reason, to thwart imposters...
@dangillmor I am nobody of consequence but would not wish anyone else to share such fame 😀