As to how long he could live, I always recommend finding out his parent's ages when they died and averaging the two together, and taking into account sibling ages of death and children ages of death. His brother, Henry, died in 1981 at about age 77. His father, Frederick, died in 1941 at about age 62. His mother, Eva, died in 1956 at roughly age 76.
So he'd already beat both his parents lifespans, albeit with access to better medical care, and his brother's lifespan only to die because of negligence. What a shame.
Based on that, I'm not sure how much longer Mel Blanc would live. He could very well live a few more years. He could live to be 100, though I'd lean towards him dying somewhere in his 80s.
He made it to what? 81? The question here really isn't how long he could have gone on, but rather what sort of shape he'd be in during that those last years. He was working up until falling out of bed at 81, but that doesn't mean he'd be "all there" when he was 82 or 83 or 90.
I'm sure many of you remember Don Knotts, aka Barney Fife. He had a lengthy career working well into his 70s but he was also going slowly blind and had breathing difficulties. Towards the end he'd occasionally do a small cameo, take a bit of voice work, or appear on stage for a night. Anything more was simply too difficult. Then there was that TBS special celebrating an anniversary of
The Andy Griffith Show Knotts appeared in, I say appeared in because he didn't and couldn't participate much.
Some of you with elderly relatives or friends will be aware that people past a certain age have "good" days and "bad" ones. When the anniversary special was taped, Knotts was having a "bad" day. He was distracted, almost confused at times, and came across as incredibly frail. They limited the number of questions he was asked and the amount of time he was on camera.
I guess what I'm trying to point out is that, while Blanc might live to 100, it doesn't mean he'll work to 100. After a while, you just can't cut it anymore and his family will keep him from making a fool of himself.