Advertisement is a bad model for niche content creators anyway. Selling "premium" content, contract work, and donations are how most are paying their bills.
EDIT: And PewDiePie won't disappear. He provides the perfect wish fulfillment for kids that would love to stay in their bedrooms and be paid to play videogames all day long.
No way can he sustain the attention beyond his 30's. His demo will grow up and he'll eventually be a creepy old guy the next generation isn't interested in.
Many celebrities and entertainers can bring their fanbase with them as they get older. This is literally what people like Leno and the Rolling Stones do.
There will always be new children who will go to youtube and find the most popular youtuber...unless he gets burnt out or feels he has enough money, he's going to keep raking it in.
Ironically it's easier to use YT as free advertising for your own content - and have YT pay you for it, even if the pay is a joke - than to rely on traditional ad revenue.
Maybe if YT wasn't so fixated on ad revenue it wouldn't be missing out on a huge potential market.
