I for one LOVED wave and used it every single day. My friends and I spent many months looking for a viable replacement. fwiw we settled on glassboard if anyone else liked wave and never found a suitable replacement.
it doesn't have threaded commenting which is sad, but the mobile apps are much better.
Google Drive is such a major part of Google strategy, that it seems remarkably unlikely to suffer the same fate.
And if it does? Google's deprecation and data export policies have on the whole been handled fairly well.
I just see a bunch of people still sulking about Reader and bringing it up at every opportunity. I too was sad to see it go. But Wave? It never got traction and even that was open-sourced instead of just being shuttered. The other examples you give aren't terribly persuasive examples either.
I can think of many smaller companies who've dealt with this much more poorly. I'm fairly complacent about Google on this issue.