You... kinda deleted the OS.
The TI-Nspire OS is around 9 MBs (see
here), and deleting something arbitrary like "os.img"... well, I don't know what you were expecting.
What's interesting though is that you got to see this "os.img". Could you tell us
exactly how you did all of this, what you saw, etc.? Be VERY descriptive - you might have found an interesting bug for us to play with.
Anyway, just reinstall, and don't delete os.img
For TI-8x games, no, we don't have a working emulator yet. calc84maniac had a project like that, but he lost all the source code.
I might port SDLWabbitemu to the Nspire, but it would be kinda slow... only time will tell.