All IntelliJ run configurations disappeared

You can try to restore your Run configuration using the Local History feature of IntelliJ IDEA.

If you are using .idea directory based format, then your configurations will reside in workspace.xml file under .idea directory, invoke Local History dialog from the .idea directory right click menu in IDEA Project View, select the label some time before the crash and revert the old copy of workspace.xml.

In case .ipr file based format is used, your configurations will be stored in the <project>.iws file in the project root which you can restore in a similar way.

If the configurations were Shared, they are stored in .idea\runConfigurations directory as separate XML files or in the <project>.ipr file (if old project format is used).

If the Local history is blank and you are in Windows, try Restore previous versions right clicking the workspace.xml file or the <project>.iws one in Windows Explorer.

To me, this frequently happened on switching branches. Turning off "restore workspace on branch switching" helps to prevent the run configurations from getting lost.

You can go to your main project and right click on it, select local history --> show history. Find some point in time where you think that system was stable (before crash) and click revert. This worked for me.