Make it seamless for people to migrate. Duplicate comments/posts/vote API calls to Lemmy. Then they could just drop the Reddit side whenever they want, and users wouldn’t have to do any work. Most wouldn’t even notice the change.
Of course they’d have to keep the app up in the meantime, but I’d donate to that fund.
The easy way is to just put whatever Lemmy instance they prefer in a webview, but I guess that would stick out like a sore thumb on iOS and wouldn’t offer the experience users are used to. Probably be better to just call it a day, take a long holiday and maybe start a new project later (or just get a regular 9-5 job). Apollo has been part of his life for about a decade, I wouldn’t fault him for just moving on.