Ha...! All this Ghirahim talk and I wasn't alerted? And it's the same misguided talk I've had to snuff out in my thread with reason. I'll shed some light on everything for all of you, all I charge is your willingness to step into the light. Here we go:
On Ghirahim's Current Status
We cannot confirm or deny whether Ghirahim is dead or not, for simply, it was not said either way. But we can always conjecture, but even granting this level of speculation, there is more logic to thinking he is still alive, rather than not. Consider the way in which he "disintegrated", he did so after you sealed his master (actually, even before so). Not only was Ghirahim unharmed, but Demise was not put in a state that he was not in before. In fact, if Demise being sealed causes him to die, then the whole plot of Skyward Sword would cease to exist, eh? Not to mention, looking at the "disintegration" itself is ambiguous in and of itself, for it didn't look like a typical death, in fact it was rather understated compared to even most death's, but again speculation, but pointing out that there is more interpretation than certainty on the subject.
On any further appearances
Ghirahim does not rely on the above topic to sway in the way of "MIA" for him to appear again. Not at all, in fact, even if he is MIA, I'd predict we'd see him again not in the FUTURE but in the PAST. That's right, anyone who plays Skyward Sword will plainly know that Ghirahim and Demise have a past together, and Ghirahim has existed and served him in his initial reign. There has been official comment as well referring to past Link's before the Skyward Sword Link, as in, for some reason, we are made to note that Skyward Sword Link is not the beginning. Suggestive to say the least, which means Demise will be returning, especially considering he has his main appearance unaccounted for. So if Demise is there, and Ghirahim is alive and his weapon at that point... would we see him? The answer is
yes.
On Zant
Comparing Zant to Ghirahim is like comparing an apple to an orange because they are both fruits. As others have said, Zant is decidedly one-shot, and had no intention of being hijacked in the end of the story, in fact there are those who were displeased with Ganondorf's role right at the end, but I won't address that directly. Zant also was not fleshed out and given as much attention to Ghirahim, this we can verify in three ways, (1) by the number of appearances (2) the degree to which he was fleshed out in comparison to Zant, and (3) Miyamoto saying that Ghirahim was designed to be remembered (for what reason, if there is to be a notable one, is unknown). Also looking onto the prior topic, one can know that while there is practically nil chance Zant will appear again, we can probably expect a Ghirahim appearance of some kind, or at least pin a higher probability on him.
Hmm... any objections?
As for the necessity for a new Zelda representative, that is highly controversial, and I can in no way state a case showing this necessity. He simply meets Sakurai's requirements and has demand, no more, no less. The best lead is Sakurai's prior intentions of adding in two Zelda characters to Brawl, comprising two of the seven forbidden data pieces on the disc, but the utter lack of information as to why they weren't added, or Sakurai's views on the topic, make it a bit wanting.
