Tony DiTerlizzi is in significant part why I got an A in A-Level Fine Art (which was then as good as you could score), because his art was so inspirational to me personally, it kept me excited about Fine Art-style art (together with
Velasquez and a few others), and attempting to replicate the style and create my own stuff in it taught me a ton, and it also expanded my ideas about what good art could look like.
On top of that, his art in Planescape was unquestionably what got me, and thus my group, back into AD&D after Planescape came out. If it wasn't for that we'd certainly have abandoned AD&D/D&D entirely for the rest of the 1990s, because nothing post-Planescape was particularly inspiring to us, but Planescape was enough, and then we got a lot of the other later-'90s stuff because we were still playing AD&D. Otherwise it'd have been WoD and Cyberpunk 2020 all the way I think, together with a few other games, and I doubt we'd have been keen on 3E. It's even possible we'd have drifted out of RPGs entirely, though I somewhat doubt it.
I really hope we see more from him in the next few years of D&D. I'll be honest - I would literally buy any D&D product he worked on significantly - in actual physical format too, so no doubt WotC would get a double-sale from me as I'd want to buy it in digital as well.