That's unclear. You may need an experienced immigration lawyer to intervene at this point, since an oversight can take place and the file may be misplaced. An experienced immigration attorney should know where to do an inquiry.
The most difficult part is now behind you. My suggestion is for you to contact the US Consulate in Guatemala where he applied for his visa and ask about the procedures and timing now that his waiver from USCIS is approved. It is usually quite simple - he may have to get a new medical exam and have his fingerprints checked again, but then he will go pick up his passport (or have it mailed to him) with the immigrant visa in it! Congrats!