I have no idea what happened here, but the layout editor is simply gone. I switched to a new tab for a few minutes and clicked Run All when I came back to test something, and Construct crashed -- after another try I realized it was because the layout isn't there anymore. There's only the event sheet editor, and seemingly no way to get back.
I've looked through every option I can find and I can't seem to bring it up... This is probably something really simple, so forgive me for being so noobish. On the off-chance it isn't, though... Am I screwed?
I experience from time to time that the tabs below (to switch between the layout and the event sheet) are simply not drawn when opening a project. Opening another layout or creating a new one and then going back to the one I want to work on, solves this. But this is only a visual issue, the layout is still shown in the Layout folder of the project tab, so this might not be what you experienced.
The persist file has no effect on the integrity of the project. It's just an xml-file containing informations for the editor's layout with the cap it belongs to. If it's missing the default editor's layout is used.