If it's been that long, the chances are extremely low that it will ever show up again. If it was stolen, it's highly likely that it was simply wiped and resold by now.
I suspect that simple 4-digit passcode lock can be cracked by someone who knows what they are doing, but the motivation of a theif is usually to quickly sell the device, not access your data.
iCloud doesn't locate your device on a map until you try to do so on icloud.com. For privacy reasons, it doesn't maintain any history of where it has been prior to that, unless it was placed in lost mode by the owner. If it's offline or doesn't show on the device list, you will not be able to locate it or see it's last location.
If you delete the backup, it only keeps someone from restoring it to the device (which can't be done anyway if it is incomplete). It won't delete anything on the device.