If you were an engineer back before Stack Overflow existed, you probably have a different take. Before SO I searched for info/answers and found them. After SO nothing important changed. I mean the web evolved in good ways and bad ways and SO reflected both, but overall I was getting my job done effectively before SO, then with SO, and don't worry about post-SO.

Only the location of info will change. The same info will be available because the same people will have the same questions and answers and desire to share. The public good is the sharing, not the platform. The people will still be around.

The next platform will be better in ways and worse in others, but that's the same that can be said about any platform supplanting another. Personally I've always stayed away from SO as a contributor because its whole reputation game turned me off. Maybe the next platform will make me more likely to contribute help rather than only consume.

As for losing the history of data, there's good and bad there. I highly doubt anything important would be truly lost. It would be rebuilt. And in the process, a lot of noise (ambiguously obsolete/incorrect info) would get cleaned out, as a benefit.