My main comment has some hard numbers based on my own experience: https://news.ycombinator.com/item?id=30889474
In short: 77% of the discs I ripped after ~15-18 years had minor issues as demonstrated through read errors (when ripping with ddrescue) and checksums (in png, zip, and gz files; I did not manually checksum files back in the day). I was able to rip 99.88% on the worst disk, and I estimate that about 97% of the files are intact on that disk. CDs and optical discs more broadly seem to be reasonable, but I'm not really sure they'll be in good shape after 30 years. I'd consider them part of a backup strategy, not an entire backup strategy. I personally use a combination of external (magnetic) hard drives, flash drives, and optical discs for backups. Replacing the optical discs after 10 years or so seems prudent, as is redundancy and/or par2 files.