Yes you would have to extract while in windows as far as I know!! If you current Hard drive/SSD what ever it is still works you can clone or Image it, Clone straight over to new drive from old drive Image create a Image of the entire disk and restore that image to your new drive. I use Macrium Reflect Free for these operations. You'll have to read through
GPSDX install thread to get how to do it all UEFI which is how you notebook came from the factory. Here is another Thread that might be of some help to you
https://rog.asus.com/forum/showthread.php?83713-G750-G751-G752-Series-Useful-Threads and this one. If you can't sort out what to do from these threads your probably better off having someone that does understand what needs to be done handle it for you.
Before you can do anyting you need to figure out what your Port 0 set up is. like I said some G759 came with 2 128GB in raid zero I guess the plan was to make them faster. I don't remember what the adapters set up was but as I remember it, it was propriority not a normal 2.5" drive set up. Yours may not or may be I have no Idea. I don't remember any G750 that came with 2 750GB in RAID Mode Someone migh have done this on there own Still the C:\ Partition can be copied and partitions for UEFI can be created on a new single SSD or Hard drive. and made bootable some knowledge is required to do this GPSDX explains that all very well in his threads. Again like I said if you don't get it, your probably better off having it done by someone that does understand what is required.
One other thing, if you sent to Asus Repair they should have sent you back a working notebook? unless you declined the repairs they offered you? If not then PM cl-albert or bhaz perhaps they can help you with the Service Repair situation?
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro