M4-78 for scrapped for time constraints. Planet itself was even shown in the game's official trailer few months before release - I believe the trailer was first shown at E3 a week before droid's planet was cut.
Saying "50% different story" is very misleading, as only things left in game files were some main plot points. I'm actually gonna go into some details on what was left, as I don't know if I ever properly explained it.
What was left of the story was the fact that Vash was there with her Padawan, M4-78 was offline (shut down by the Sith) and you needed Archon's permission to reactivate him and that Environmental Zone - and the control of ES-05 - was taken over by Kaah who's gone mad. Also the fact that Sith were pretending to be the colonists but were dead by the time player arrived.
Actually, most of Kaah's dialog in the Environmental Zone, when he's pretending to be ES-05, were Obsidian's. I did some rewrites but nothing major.
There were some voice overs for IS-24, the Industrial Archon. He only had 10 lines recorded though, compared to 60+ in M4-78EP.
Obsidian left a very brief dialog with the other Archon, ES-05. There were just some basic questions - who are you, what do you do, something about Kaah, asking about re-activating M4-78. Some of left-overs lines for her were used in M4-78EP, but I had to write a lot of dialog on my own. Same situation with Kaah.
I thought there were some lines left for LS-44 (Landing Arm droid) as well, but I can't find any now, so maybe I'm mis-remembering something now. I thought there were some lines for him informing us about radiation, but I can't find them.
Radiation idea itself was also Obsidian's; Vash, Kaah and IS-24 all had lines about it.
There's also a datapad description saying that re-activating four power stations in the Central Zone would increase L5-65's effectiveness. We ran with the idea and tweaked it, so it was required to re-activate them in order to proceed. I don't think we'd have had that puzzle without original datapad's description.
Also, there were bunch of puzzles but they were all moved to Goto's Yacht right after the planet was cut (the Yacht itself was designed in less than a week, IIRC, and it's possible it would be scrapped as well if they couldn't move M4-78 puzzles).
And that's pretty much all there was for the planet. There was not a single line for M4-78 himself or any proof that we were supposed to talk to him (though what are the chances we weren't?). No indication of any kind of "droid's quest" for clearing the radiation (although tlk has some lines that look like their supposedly HK-47's, asking about M4-78). No conversation with any other droid, or any indication of what each place of each area was.
Industrial Zone was also most likely supposed to be more combat heavy, at least in the end, since player had an option to ask IS-24 "Why did your droid attack us?" or something along those lines.
So anyway, there was maybe 10% of the planet left, but that's being pretty generous