Mark Seibert's music is, IMO, a key part to the magic of the Sierra games, especially the KQ games. His simple but beautiful melodies helped define the atmosphere of King's Quests V-VIII, and he's at the height of his talents in King's Quest V and King's Quest VI--arguably two of the most well received games in the series.
I believe a KQ game without Mark Seibert on board would be like a Star Wars film without John Williams, or a Sergio Leone film without Morricone--It just wouldn't be right. There's a beautiful simplicity to Mark's music in the KQ games that really just belies the magic of the series--A beautiful, sweet simplicity.
His songs aren't ten minute epics, but little, atmospheric melodies, and even though they're simple, they lift simple VGA scenes (in V-VII) to emotional heights. I think even some of KQ8's staunchest opponents would be hard pressed to argue that Mark's music in KQ8 wasn't a highlight of that controversial game.
So, please--I know some Telltale people read this--Could you resist the easy path and the temptation to use your own people, and consider giving Mark Seibert a call?
If not Mark Seibert, than at least get any of these guys:
Jay D. Usher
All of the men listed above helped craft the music of King's Quest V, VI and VII and are just as important to the atmosphere of those games as Mark was. So if Mark isn't available, at least offer the gig to one of those guys.
I think that the addition of Mark or any of those guys to the team would not only would it make TellTale's KQ feel more like the originals, but it would also help recreate that unique King's Quest atmosphere, and most importantly, it would make a lot of KQ fans--even the skeptical ones, I would imagine--happy.
So please consider this.