Do I need to replace the wall after a shower head leak?
Chances are very good that the inside of the wall is just "regular sheetrock", and that will have gotten very wet.  That fan setup is pretty cool and should dry it out since you were smart enough to cut a hole in the ceiling.

Mold grows in areas that get wet and take a long time to dry.  If you can quickly and completely dry out a surface, it should be fine.  Once it's dry you can spray a mold preventative in the cavity just to be sure.

More on the sheetrock...  Builders use "green rock" (many names, but the front face is green most of the time) in wet locations.  The front face is moisture and mold resistant, but the back of the drywall is plain, brown paper.  Your water hit the plain paper.  Many remodelers will use a cement board to replace the old drywall because it's a much better material that they can warrantee, but only a very high quality builder would use that, and chances of it happening go down with the age of the house.