Honestly, there were signs early on that Debby's presence has been a great help to MC. And while ships will be ships, I think they have been helping each other during all this. Happy to see him able to say it clearly.
Why yes, the plan IS to keep playing with Debby until he's an old man. Including old people stuff like Gateball.
If she gets worried about being lonely after he's gone, she can just have a child or two with him. Or more, if they feel like it. They could play games like "who's educating our child better" or "who's the child's favorite, mommy or daddy?" or whatnot.
Even science experiments like "Can a human and a devil even have a child?" or "How would such a child turn out?" Maybe have multiple kids in the name of science.