In exploring the Adobe documentation for Premiere Elements 11, the Replace Footage description caught my attention.
especially the part about replacing the footage, but still retaining the edits that were done for the footage that was being replaced.
The above is the lead in for my focus on Replace Footage and its use when the Media Offline sets in for a project whose source media have been moved after the project was saved closed.
My suggestion (and still is) use the "Where is....?" messages to reconnect the missing media. These "Where is ....?" messages will appear when you try to open this project whose source media have been moved after the project was saved closed.
But, if you opted out of those messages with the Skip/Skip All Options and find yourself with the opened project populated with Media Offline colorful displays, one choice to reconnect the missing media at this stage is via Replace Footage.
(a) In Project Assets, right click the thumbnail with the Media Offline display and select Replace Footage.
(b) Browse for the original footage that was imported in the project and select it.
(c) Repeat as necessary for any remaining Project Assets thumbnails with the Media Offline display.