there will still be a fine oil layer covering over all the surfaces, enough to prevent any rust from forming, just don't leave the "open" engine exposed to the elements, ie in open dusty air or moisture.
at motor workshops where engines are stripped down for repairs, they also stand for extended periods of time without any oil in the sump, awaiting some or other spares (gaskets etc).
your biggest issue is allowing foreign object damage to enter the open wound on your engine (tappet cover) and most likely in the form of dust and moisture.....a day or two without oil in the sump isn't going to make any difference....just don't start the engine!!