Whatever you choose to do, get onto another provider and test it.
Get a similar instance on AWS (or gcloud or ...) and try it there, keeping the disk and then attaching it to another instance as additional storage and scanning it. dd if=sdb | hd
Just about all of your sensitive material should be in
It is the config files with embedded passwords that bother most people.
If you know what they are, search the whole filesystem to root them out.
rm will delete files, but a hex editor will still read the disk. So zero afterwards. Have a look at shred. You should have a log of your config files and where they are for DR purposes right ? Don't forget crontab files if you have passwords in those, say.
The CentOS install, or any ramdisk solution is sound. The kernel will be in memory, you need dd and some bin content. But if you reboot in recovery mode you may not have networking or SSH and cut yourself off.
N.B. Kedare has a good idea, and if you are running from ram on your next reboot (ramdisk) this is possible, it is very hard to recover from /dev/zero writes to begin with so it does not really add value unless your life depends upon it ?