That was a thought I had today as well. I think a lot of that could be assumed. Maybe Boba would’ve negotiated with Jabba about keeping Luke, but once he killed his Rancor he wouldn’t be able to convince Jabba to hand him over.
3PO’s line about them being slowly digested over 1000 years implies they won’t immediately die if they’re cast into the Sarlacc, so Boba might be planning to retrieve him later, like your idea explains. Perhaps 3PO’s line could be altered to be “slowly digested alive for over 1000 years.”
I think an important thing about the new Boba/Vader scene is that it acts as a segue between the opening scene and the rest of the Jabba sequence. But it doesn’t seem like Jabba decides to throw them into the Sarlacc until after Luke kills the Rancor. Perhaps you could have an additional communication scene between Vader and Boba before the Sarlacc sequence where the dialogue plays out as you have it.
You could use the same shots as the earlier scene, or Boba could be sitting in his parked ship communicating with a Vader hologram. You could use shots of Boba in his ship from ESB. You could even use the establishing shot of his ship in Jabba’s palace from the Book of Boba Fett (I personally would rather avoid using any modern shots, but you could probably rework an ESB matte painting of the ship to suit this idea.)
But like I said, I think you could deduce that Boba would either retrieve Luke from the pit, or that he knew Luke had something up his sleeve. I worry two Vader/Boba scenes might push it, but maybe it wouldn’t. That could be something we could test out. But I don’t think it makes sense for them to discuss the Sarlacc in the first scene. You could push their single convo to before the Sarlacc sequence, but like I said, the whole point of their first communication scene is to have the opening scene and the Jabba sequence flow together.
You also have to find appropriate Boba dialogue for this new idea. This is just my preference but I’d like to make any new Boba dialogue worth with the Jason Wingreen voice as well. I don’t know until I can experiment, but I might could get this line to work with both the Morrison and the Wingreen voice.
“Don’t worry. He’ll survive.”
Then when Vader’s hologram goes away, you could have Boba turn to look at a hologram/diagram of the Sarlacc.
Or maybe new Vader dialogue could be constructed to where he tells Boba to pull him out, since there is generally more Vader dialogue to work with, but I guess it serves Boba’s character better if an incapacitated Luke out of the Sarlacc is his idea. I also had considered a scene where Boba could say something to Jabba, but I don’t know if the shots of Boba leaning in close to Jabba are long enough to establish anything.
Anyway, not trying to be negative on the idea. I like the idea. I also want to be careful not to overthink/over-explain stuff. I do like that it could be it’s own scene that can be plugged in or out depending on people’s preferences. I also would prefer if any new shots fit the time period of production and not too modern, but that’s just me.
And that’s a good point on how this all affects the Emperor and Vader’s first interaction. I do have some thoughts I want to share later on Vader’s characterization and the characterization of others.