There is no way to restore your edits, hence the explicit warning by LyX:
As you have observed, LyX clears the undo/redo stack in such case. I was hoping that one of the backup files LyX generates may come as a rescue: Depending on the settings, LyX keeps for each file
doc.lyx two backup files:
doc.lyx~ is copied from
doc.lyx before a Save command, so that it always contains the previous generation and an accidental Save command can be undone.
#doc.lyx# is generated by LyX's autosave feature, usually every five minutes.
However, when issuing a Revert to Repository Version, LyX unfortunately deletes
#doc.lyx# and overwrites
doc.lyx~ as well with the repositry version.