Being a lifelong Laker fan, Fisher missing the 0.4 then the Lakers probably lose the series. The year before though, Robert Horry missed what would have been a game winning shot in Game 5, and if he'd made it the momentum gained from the shot probably would have meant they'd beat the Spurs and go on to win the title.
As for the fate of Shaq and Kobe, only winning the title of 2004 could have possibly convinced either of them to stay. The whole Colorado rape case and the ensuing drama that unfurled was like nothing else even a city like LA, known for its internal drama, had ever seen, and by that time the Shaq/Kobe relationship was beyond saving, sort of like by the late 1980s it would have been close to impossible to save the Soviet Union (interestingly, Greg Popovich, coach of the Spurs, compared the Laker breakup in 2004 to the collapse of the Soviet Union).
Malone and Payton were both at the end of the line by that point, and besides, Malone was injured at the latter part of the year so it probably wouldn't have made that big a difference in the big picture had the Lakers kept Robert Horry instead of letting him go with the Spurs. Gary Payton also never fit with the triangle offense, and plus he also took time from Fisher, and the reason why I believe he left the Lakers for three years after the season was over.
Thus, more than anything else, the Lakers of 2004 destroyed themselves from within more than the Pistons beat them in that ill-fated series. There was also the underlying issue in that Shaq wanted a contract extension of nearly 30 million a year to 2009, and that Kobe was going to be a free agent after 2004, and Jerry Buss, having to make a choice between an aging Shaq and Kobe coming into his prime, he decided to trade Shaq.
Its too bad though, considering that the immediate post-Shaq years coincided with Kobe's prime, where he largely wasted being forced to play with the likes of Smush Parker and Kwame Brown...
If Shaq and Kobe would have stayed together, it would have been utterly unfair. For instance, Shaq and Kobe decided to get along in 2001 and then they proceeded to crush the Blazers, Kings and the Spurs. 2003 was an abberration, and had Shaq and Kobe managed to get along in 2004, so long as you had Derek Fishers, Robert Horrys and other solid role players around them they'd have crushed the Pistons, and also win most of the titles from 2005-07, as that was before the 2003 class came to prominence and that aside from the Spurs, there was no other teams in the West that could have beaten them in a seven game series, never mind a much weaker East. By beating the Lakers in 2004, Detroit was a perennial Eastern Conference champion for the next 5 years, and if it hadn't happened they'd have quickly fallen into irrelevence like the Nets and the Sixers had before them, and the Heat probably would have remained a middle of the pack team.
Speaking of Derek Fisher, it wasn't surprising that he hit a clutch shot. It was what he was known for throughout his Laker career (like the game tying 3 vs Orlando in Game 4 of the 2009 finals, his Game 3 performance vs the Celtics and a whole bunch of clutch shots). Though he was slow, short and couldn't jump, he was a great leader and the only guy for like 10 years who could walk up to Kobe and say f-you to his face and Kobe nodding his head in acceptance, and also one of the only true friends he has ever made during his playing career.
In the big picture though, so long as the Lakers managed to keep Kobe after 2004 and the Laker front office having any sort of competence, the Lakers more than likely end up competing for a championship again sooner or later, as we saw in 2009 and 2010 when they won the title.
We can also make the conjecture that what would have happened if David Stern hadn't blocked the Chris Paul trade, which would not only have given the Lakers the best point guard in the league in his prime, but also saved the Lakers millions of dollars. Then again, the Lakers did end up getting Steve Nash, so yeah, being a Laker fan isn't all that bad at all.
(Speaking of which, Bill Simmons, an avid Laker hater, always seems to complain about how the Lakers always seem to get great players for trash)
http://www.grantland.com/story/_/id/8182261/game-nba-thrones-part-i