There have been times when I'll perform some editing task and for some reason objects just disappear from the screen afterwards, and I know they should still be visible.  A typical reaction is to use the UNDO command and replay the editing scenario and hope they appear a second time around.  Hold your horses, if you issue the REGEN command, the objects usually re-appear because the video card just didn't catch up with the file.  There are times when objects don't disappear, when they should, and the REGEN fixes this most of the time also.

For those oddball occasions where the REGEN or REGENALL commands won't make the objects re-appear, try the AUDIT command.

A classic example is when you edit a 3D block with REFEDIT and the instances that aren't being modify disappear, as they should, the REFEDIT command closes and the hidden objects don't re-appear.  Those objects are still there, but only a quick AUDIT will return them without closing and re-opening the file.