I agree that it's sad that Han Siwon soul is dead but it's not that it is irrelevant since Taemin needed a body to switch with...
But why did Tae Min NEED a body to switch with? Why couldn't he have met up with Woo Jin, again, like, say... in the NORMAL way...? It would have made MORE sense to do it that way then this way... after all...? And why did Si Won NEED to die in order for Tae Min to switch with him? That question answers itself, BTW.
Why why why... why not create your own manhwa with your preferred plot instead then. Why did they even need to separate in the first place? Why did taemin need to die and switch body? He should have just died right then n there and end the story! Why can't tae min resurrect himself? Tae min should've revived as a zombie! That would make the story more interesting!!!
I think it's still too early to judge and say Han siwon is irrelevant to the story. We still don't why he's bullied and what's up with his brother and who was it that raped him. Since han siwon has all these problems & seems to be incapable of protecting himself, we get to see this being turned over when tae min and siwon switch body. Although the "han siwon" now is tougher, he's still not as strong as the original "tae min". There's also still lots of things tae min does not know about siwon and the school. Compared to their chilhood, tae min is now the weaker and more vulnerable one than woo jin, so now they have sort of switched roles. All the drama is just for the plot anyway. Tae min didn't need to switch body, maybe they could've meet again normally, but that would be the plot of another story, not haribo's.
That is fate.
It's actually kinda funny since 'Han Siwon' was made and introduced that he's bullied, and then he died, just to make Taemin switch his body to siwon's. he's actually irrelevant for this whole story and has nothing to do with the main couple at all. It does make the stoty interesting, but I feel it would be boring if he's really dead, and all that left would be the main couple （￣へ￣）