Systems Deployment

We need a little more info I think, but I would say that in your case you simply don't include the preinstall task that wipes the drive.  If the target machine already has the two partitions, then point to them with your image task.

If wiping the drive is ok but you're just worried about going from two partitions down to one, your diskpart script can be configured to create the two partitions again at whatever size you want.

This is where a Kimage shines.  When we get demo units in and want to return them to the original image.

Capture your image and then you can redploy it to the same machine without reformating by checking one box

Note: We did not sysprep, this was for backup purposes only, casting that image to multiple machines would result in duplicate SIDS.