Is there an easy way to create a corner from disconnected edges? I would like to find an easy way to make Picture A look like Picture B without recreating the cube.  I can do this manually by removing faces and recreating the corner but it takes a lot of time and I have several models I need to do this on.  The target angles are all 90 degrees and all of the faces should be the same size.

Picture A


Picture B
Supposing that you have all non-instanced cubes, with different grid size, etc... so you can't use any trick and you have to model by hand your corner, there are two operators that can may help you:


"Run the previous action" (Shift+R) with automatic merge enabled
Grid fill


I'll start by deleting the messed part and than pick one of the edge path by selecting two vertex (Crtl+RMB), extrude once by snapping to the vertex grid, repeat with Shift+R several times and complete with a grid fill with appropriate parameters.