Gah!

[Oshyan]

It seems very surprising that the file would be completely gone. A corrupted file would be less strange. Have you searched your entire system for the .tgd? Is it possible it was saved in a different location than you expect, as Peejay mentioned for example?

- Oshyan

[Yoda Almighty]

I suppose it's possible, but t's also possible it somehow got moved to the trash, and I inadvertently deleted it 

[Mr_Lamppost]

TG remembers the last directory you saved to or loaded a file from so check your object or texture directories, your scene may just be in there somewhere.