do messages back up in icloud

This might help you understand what is backed up in iCloud.

About backups for iPhone, iPad, and iPod touch - Apple Support

iCloud does not erase messages unless you delete them on your device and then backup again, or unless you disable Messages with iCloud, assuming that you were doing that in the first place.

I think you need to provide some context and more detailed information so we can determine exactly how to advise you.

If you set up your phone to do so, yes

To enable iMessage Sync to iCloud go into settings > account > iCloud(your main iCloud account)> iCloud and you can toggle it from there

If the messages were deleted then you are out of luck unless he backed up before deleting them