That's sad and interesting to hear. Hopefully there's enough material to be published.

There's also this: https://www.amazon.com/Extreme-Metaphors-J-G-Ballard-ebook/d... ("A startling and at times unsettlingly prescient collection of J.G. Ballard’s greatest interviews.")

I didn't read it though, just know about its existence from following Simon Sellars (of ballardian.com fame) on Twitter.