I wouldn’t bet on an eBook being usable 30 years down the line.
I wouldn't seriously bet on an eBook reader being usable 5 years down the line. Could it? Possibly. Is it guaranteed? Not even close.
As for the content, my SO points out that we have knowledge that was stored on computers in formats nobody alive knows how to read anymore. We've lost information—some of it probably very important!—that's younger than I am.
In the mean time I'm reading stuff that's been gleaned from writing that was recovered literally thousands of years after it disappeared.
Thankfully I've never lived anywhere where prom night is a thing. I can't imagine the stress of "keeping up". It was bad enough having the high school "cool kids" cults; amplifying it would be a nightmare.