Beside the discussable mortality rate among healthy adults, and beside surving with permanent lung damage, many people who are 30-40 have kids who are 0-10. Things take a whole new dimension there.
No one under 10 has died from it, and only one person under 20. The mortality rate for people under 50 is about .2% (compared to 2.3% for all cases).
So far it's basically a logarithmic function of age.
The lung damage piece is obviously frightening, and we obviously still have a lot to learn about it as we're not sure why children are able to fend it off so easily yet.
As for permanent lung damage, it's hard to say. From what I've read about ARDS, as expected, if you're young, lung function and general physical function can improve back close to baseline over time (e.g. 5 years). So it's not like you're going to be confined to a rocking chair but you won't be winning any marathons either.
EDIT: sourced: https://en.wikipedia.org/wiki/Pulmonary_fibrosis which we saw in SARS coronavirus-induced pulmonary fibrosis.
> There is no known cure. [...] Life expectancy is generally less than five years.