Reason "Operation manual", page 404:
About “Orphan Audio Streams”
If your computer should malfunction (due to power loss etc.) during recording into a previously saved Song document, there is a good chance that your last unsaved audio recordings can be (at least partly) recovered:
1.Restart your computer and launch Reason.
2.Open one of the Song documents that was open during the computer malfunction.
If the Song contained unsaved audio recordings, Reason will find these and show an alert saying that the Song contains “orphan audio streams”. You will be given the choice of deleting them or having them appear in new clips on a new audio track, for salvaging.
! Note that it’s only audio recordings that it’s possible to recover. Any new Instrument Tracks in an unsaved Song will be lost in the case of computer malfunction.
So, audio data may be recovered, instrument data does not. This is why my PC gets its power from an UPS...