The problem is that existing customers don't "have" anything. They stream the movie on demand from Sony's servers. And Sony can't keep the movie on their server anymore. The entire delivery model is broken.
Look how it works over at Steam. If a license expires, even if the publisher goes out of business, Steam removes a game from its storefront, but the files are still on their servers and they keep them available for anyone who purchased a license. I think the only cases where they actually removed files from their servers and blocked redownloads were when there was an actual legal or liability issue forbidding them from continuing to offer the files (for example if they contain malware).