Without GIT, there is always a backup copy of the .lfm file in the backup folder (or whatever backup option was selected in "Tools" > "Options" > "Environment options" > "Backup"). Of course, the file must have been saved after the "desaster"...
As already noted by af0815, you can also try an "Edit" > "Undo", but this is not implemented by all property editors. And sometimes the menu command is grayed while the key combination (CTRL+Z as noted by af0815, or ALT+Backsp in the classic key layout) still is possible.