If you lose the contact with the System i, you will get the message 'Lost connection to host' and the designer will end. But do not worry: A backup of your overlay is on your PC and you reload that design when you restart the designer (after regaining contact to the System i).
Important:
To make sure, that the local overlay is kept, you need to make sure, that the designer is ended abnormally e.g. via the Task manager, If you just click OK to the message above and close the designer as normally, then the local copy is NOT kept.
In that case of a local unsaved copy of an overlay the designer will start up with the message 'Found previous unsaved overlay', when reconnected.