Well, if Kasparov beats Shirov, then it leaves it exactly where we found it: with Kasparov, the world number one, as champion of his own organisation, with no formal rules to determine his challengers, and the International Chess Federation, Fide, running a lame "official" championship for the title currently held by Anatoly Karpov.
In the less likely event of Shirov beating Kasparov, however, it is doubtful that he would generally be accepted as world champion. He would still be rated behind Viswanathan Anand, and, having failed to win the Fide world championship in January, would also need to establish his supremacy over Anatoly Karpov.
The mess that was created in 1993 when Short and Kasparov left Fide to run their own match is still a long way from being sorted out. The status of world champion can only be restored in a unifying match, and the sooner the better.
Here's a composition by a true world champion: White to play and draw by Vassily Smyslov. With Black threatening gxf3, and 1.fxg4 losing quickly to 1...Kxg4 followed by f4 and f3, White's task looks hopeless. Even 1.f4, hoping to get at the black king along the black diagonal, offers no chance after 1...Ra6+.
The solution is extraordinary: 1.Bf6+!! exf6 2.f4! Rh8+ (2...Rg8 3.Kh7 is no better) 3.Kg7 Rxh5 4.a4! Rg5+ 5.Kh8! (5.Kh7? loses after 5...Kh5) 5...Rg6 6.Kh7 Kh5 7.Kh8 Rh6+ 8.Kg7 Rg6+ 9.Kh8 and Black can make no progress since 9...Kh6 is stalemate.