Did you open the .indt by script or by hand?
If by script, then you must know where it is. If by hand, then I don't think there's any way to get back to the template. If you know the name of the template, you could search for it in a script, otherwise, you're out of luck.
I'd reorganize the script to start without a document open and have the script open the template; if it's potentially anywhere, then throw up a file dialog and have the user locate it.