There could be a saved backup within Hijackthis. Open Hijackthis, click on Main menu
then View the list of backups
. The available backups Hijackthis has made will show in the window. Select the most recent backup and restore it.
Don't have much more information about what happens once you've selected a backup. I haven't had to deal with this before (accidently removing something). Somebody will come along that maybe has had to to this and explain in more detail.