That's really sad to hear. I always liked watching Wallace and Gromit back in the day. I'd often rented the shorts on VHS at Blockbusters. I didn't know that Wallace's voice actor was that old though. At least he lived a long life. I hope that he's at peace and that his friends and family members will be okay.
He also portrayed Norman Clegg on all 295 episodes of Last of the Summer Wine during its on-and-off 37-year run (making it the longest-running live action sitcom in terms of episodes in television history).
Was quite saddened to hear this. He added so much charm to the series, especially since he was the only voice in many projects.
It was something that was sadly looming for a while, since Nick Park had spoken about his poor health previously, Sallis had in fact not been voicing Wallace for quite a while, having coached a soundalike for several modern projects and advertisements (who while obviously not quite the same, does at least seem to do the role justice). Park had in fact stated this to be the reason he wasn't sure about making anymore proper films of Wallace and Gromit since he knew how much Sallis played into making Wallace's character.
Also another Last of the Summer Wine star that has left us, though at least Sallis managed a perfect attendance record before the show ended. That's some dedication.