Missing Bootcamp partition

I use to have a Bootcamp partition, which was about 100Gb, but it has disappeared from the boot options and I am not sure if it still exists on my HD. I am looking to sell this iMac, so I was going to try and remove this partition anyway, but I don't want to sell it if someone could recover it and access my login. I have been trying *Disk Utility > First Aid* on the drive I have also been running /sbin/fsck -fy in Single User mode. This is the current situation of my HDD. 1. Does the Windows partition still exist? 2. As I didn't remove the partition/windows installation properly from BootCamp Assistant, can it be recovered? 3. If I perform the *Recovery > Re-install MacOS* for the sale, will this wipe the entire 1TB disk properly? EDIT After running diskutil ap resizecontainer disk2 0b I am getting the error object map is invalid