Yoda wasn’t coming back originally? How on earth was that supposed to work story-wise?
I would need to check in the book (easier said than done, it’s pretty dense) but I think Yoda’s mention of the other Skywalker would just be folded into Obi-Wan’s dialogue - and the Luke/Obi Wan discussion would not happen on Dagoba. IIRC the idea was for Obi Wan to tell Luke that Yoda was now one with the Force.
I’m not sure if this script development took place before or after talk about the Force ghosts of Yoda and Obi Wan appearing during Luke’s duel with Vader. Not to mention the two Death Stars!
Back to the OP - I found an interview with Marquand that relates to your question:
https://www.denofgeek.com/movies/richard-marquand-interview-return-of-the-jedi-star-wars/
Yoda dying off camera and never being seen again would have been pretty lame. In the original making of ESB book, Lucas laments he couldn’t shoot a scene for Jedi during production on ESB, as there was the issue of saving and storing the Dagobah set for the next film. What he had in mind either had not been written yet, or the need to finish ESB took precedence.