In case a page is deleted in APEX, we can recover it using the export feature of APEX. The steps are as follows:
Open the application in application builder
Export application and then select the option -export page-. from there, the dropdown list shows only the pages that are in the application. You have to select the timeframe you need.
In order to select the deleted page, you have to tweak the HTML and this is where we use firebug to modify the list in order to add the option for the deleted page
Once it is done, the export will allow the export of the page
Returning to the import/export option of the application and from there select the file that was exported and import it. The page will be placed in the app.
For a full step by step explanation , see the original post by Peter raganitsch
Recovering a deleted page in APEX