how do I UNDO an effect applied on audio AFTER SAVING and closing?

I'm a beginner,  So i just dragged some audio files in the files window, and added a Reverse on part of the audio in the waveform editor, later I just saved and closed it, when I come back later, there's no audio in the files window and i thought this is like a project and it will save all the audios imported. Also I found the original audio file has alredy been changed with the effects on it and I thought threre should be an effects controls panel like in premiere, but I couldn't find it anywhere,how  can I undo the effect or the audio file is just ruined from now on??