Since we have the Pro-Fett and the Anti-Fett representetives, I'm going to be the Semi-Fett avatar:
Keep Fett only inside the actual Palace.
Jabba has a reputation for keeping bounty hunters and thugs around his palace, especially if they please him in some way. Fett could also be hanging out there because of a recent bounty etc.. etc... who knows, basically. But, we know Fett has some relations with Jabba so it's not uncharacteristic that he could be there. If perhaps, this was Fett walking around in say Docking Bay 94, then I'd say REMOVE HIM.
So, him appearing in the background of Jabba's palace a few times is cool. Him going on the sail barge, is not cool. He'd have no reason to do that.
I also think, while it's fun to picture what could have been or just brainstorming cool side-stories, we shouldn't be writing extra or different plotlines into the movie. That's not really what Revisiting is all about. It's not Revisioning.
Let's meet in the middle, Fett in palace: Good. Fett on barge: Bad.
Now (rambling ahead):
Personally, I love Fett and hate his death scene. Obviously, he was used in ROTJ because he could be an extra action figure in the ROTJ line and his costume is cool enough to use again.
So what do we gain by keeping him in the palace?
We see he isn't above hanging out with scum like Jabbas minions and Jabba himself, as well as associating with the elite of the Empire.
A thermal detonator does not scare Fett. He feels his life may be in danger and he's ready to fight for it, regardless. The same way he was ready to pop a cap in Chewbacca on Bespin.
His calm and observant reaction to the unfolding events (rancor etc..) is a great contrast to everyone else in Jabbas palace acting like a friday night at the Appollo.
And, if omitted from the barge scene, we can draw the silent conclusion while the rest of Jabbas barbarians were lining up to watch the prisoners be uneventfully fed to a hole in the ground, he decided it was a good time to hit the dusty trail.
I think all these things lend/benefit the character more than detract from it.
On the other hand, omitting him from ROTJ all together, serves and even bigger purpose to the mystique of the character, which is exactly what made him so popular in the first place. I see that as well.