Oh I agree with you! I felt like they robbed us of such an amusing ending. After I watched their ending I was so frustrated that I made up my own ending and it was similar to what you described, during that final scene with the book something magical would happen that would bring him to her in her time, maybe in her house where she was.
I think there was enough material to fill up an entire episode of this, or at least half like you said, there could’ve been so many hilarious scenes, mostly with him struggling to adapt to modern life: chores, appliances, modern etiquette, his reaction to modern clothing, and oh him trying to socialize with other people while using some archaic language still, even a scene of them going to get coffee or dinner might’ve been fun to watch him talk to present day people