While it is possible, there is more risk and no advantage of doing so.  Hardware wise, the Optane was performing as a cache to the hard drive and improved the overall speed.  A new SSD already have similar read/write speed as the Optane and have its own cache with high performance controller.  Aging hardware may make it more riskier to use the Optane for no performance gain in return.  You can remove both of the old hard drive and the redundancy Optane, just use the new SSD by itself. Software wise, the original operating system for this machine is very old.  Since 2017, Microsoft has provided Windows updates every month and version upgrades twice a year, going back to original version will expose your machine to multiple risk and will require a lot of time to update and upgrade to catch up with all drivers and patches.  Or you can create a Windows installation USB drive directly from Microsoft creation tool, and you have an up-to-date version of operating system. Personally, I am not a fan of all the extra support and assist tools as they seem to create problems more than solving them.  Your machine is out of warranty by now, so don't be shy to support your own machine.    
Hi everyone, I have a XPS 8920 and I want to replace the original HDD (mechanical drive) with a SSD drive.  My question to this board is about the Optane memory that's paired with the original HDD.  If I remove the original HDD and replace it with a new SSD will I be able to install the original factory operating system from Dell and pair the Optane memory? I've worked on PCs for a long time but never delt with this Optane in the equation. Any help would be appreciated. 
XPS 8920, replacing the original HDD with a SSD?