Possible, yes, but pretty damming to Microsoft's reputation if proof that their infrastructure has been compromised and anyone realizes it's happening. This sort of thing killed Sourceforge when they started shipping adware bundled into installers of the programs they distributed.
I fully expect my blog on GitHub Pages to outlive me.
They're stored in the Arctic Code Vault, as well as more replicas than you can imagine, because git, so I could imagine there's very little risk of data corruption, and because of the amount of knowledge stored in this standard format of static HTML, there's strong incentive for people to preserve it and keep hosting it if Microsoft becomes evil again and decides its not profitable. Moreover, if you PGP-sign your git commits with a 4096-but RSA key, you can be fairly sure nobody will edit your commits (perhaps for at least for the first 200 years). I believe the key here is lumping your data in with other high-value data.