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/