Don't forget that GDP can go down.
And so can wealth.
Ukraine just had a trillion dollars worth of growth bombed out of existance. Coal isn't the only resource that can go up in smoke.
Historically those stagnant periods of low economic growth were usually broken up with violent strife. It can happen again of course, but does not seem likely (atm) on a significant scale. If we assume we're not all going to be bombed out of existence, then the question is whether most of us are going to be holding up empty bags when the stagnation sets in.