Killing a main film character for the sake of gaining readership and interest is like lying to get attention.
It's not constructive, it doesn't offer anything overly exciting or new, and it really does nothing more than piss people off at you.
Chewbacca has been one of the most underutilized characters in EU because few people beyond Timothy Zahn had any ability as authors to actually utilize Chewie like Lucas did in the films. The creators of Southpark use Kenny more creatively than authors in Star Wars used Chewbacca.
That's ****** up, if I may be so blunt.
And at least Kenny's killed off interestingly in South Park, so he's still one up on Chewbacca's death.
Ultimately though, the NJO's other main failing is the Yuzahn Vong. Super Villains from somewhat of a distance away who just happen to show up when it seems like everything is ok. They seem to "assimilate" at least parts of their victims. They're "unstoppable", and have no regard for other species... Blah blah blah...
Yes, Star Trek did it with the Borg first, the Breen, Species 90210 (or whoever they were from Voyager) and their organic ships and stuff, etc., etc., etc... It's a tired Sci-Fi ploy to create new threats to a played out world.
To me, Luke's resurgence of the Force and FOrce Users (and his somewhat haphazard way about it) would be enough plotline to keep new enemies arising. New species shouldn't be introduced as more of a threat than anything ever to Luke Skywalker though, as it sorta cheapens the movies and their point.
That's part of the problem though. Luke and the films are intended to, kinda, imply that Luke's faced the ultimate trial he'll face. Still there's more tactful ways to go about it.
Zahn had a knack here I believe then. He didn't need force users to cause trouble so much as he used political and military strife, and an enemy who merely was smart. The Yssilimari were kinda wonky but they weren't the Vong so I bought it some more.
I like NJO's establishment of Luke bringing about a, well, New Jedi Order... The enemies and Chewie's death were just horrible turns though, IMO, and they become really just detractors from the series.
I'd like to actually see some EU that establishes a war of attrition that the New Republic faced with the Empire. Rather than this "Warlords" and "infighting" crap with the Empire, I think the story should've been one where they actually held it together.
Nazi Germany wouldn't have collapsed had Hitler died in 1940... If anything, the Allies would've faced a much more destructive and competent enemy without him. Perhaps the Empire could've had a more fitting scenario for it.
Anyway, that's a rant I'll end here... Needless to say, EU's something I'm picky on because there's just too much BAD in there.