Wow, I'm really sorry to hear about that dude. I personally think your voice work is awesome and you really deserve a part (even if it's a small one) in a GTA game given the kind of effort and time you've put into this site. If it weren't for you, Kodo, and the other staff members, I probably wouldn't be nearly as involved in the GTA community as I am today.
I would suggest giving them a call, or maybe emailing them or something, especially if you turned down other projects after R* asked you to participate in GTAIV development. If they were willing/kind enough to ask you in the first place, I'm sure they'll be generous enough to help make up for it in some way. As someone mentioned, there's always the DLC. And if you remind them of their offer, maybe they can get you in to work on one or both of those episodes.