Short version:
Had GOG galaxy installed on secondary HDD
HDD failed so i removed it
Tried to uninstall using Windows 10, can't uninstall b/c drive is missing
Tried to re-install but can't change install location(presuming its trying to install on missing drive b/c that's where it used to be.
Thoughts?

Windows................

Well the previous location is probably recorded somewhere in the registry. Go clean up the traces.

I don't use Windows 10 or Galaxy, but have you tried uninstalling it from "Programs and Features" instead of running the uninstaller executable? When it is unable to find the program, it should offer to remove the entry.

Failing that, you can use subst to create a virtual drive mapped to a directory on your primary disc, then try reinstalling and uninstalling from there in hopes that a subsequent installation will allow you to choose the install location.

Example usage:

subst d: c:\temp

Change the drive letters and directory as needed, of course.

Success!
Thank you for reminding me of the registry and what not. It'd been awhile since i've putzed around there.
Solution: installed CCleaner, cleaned up the registry and deleted GOG galaxy through that. immediately installed after that.
so thanks for the help!

Thanks for reminding me to make sure Galaxy was set up properly!