That's why I asked on page 1 "why you're missing premolars?"
You said they were back molars (wisdom teeth), but clearly there is a black spot where your premolars should be.
To answer your question: yes it's a mistake to remove those. The proper fix if the teeth won't fix is a 3 piece to widen the arch. If the bottom teeth don't 't fit as well, it gets more complex as you can't widen the arch; but, if anything they should have tried IPR or removed the 2nd premolar rather than the 1st (more root structure compared to the 2nd and thus more bone loss when pulled).
Whether it will cause the face to sag depends on many things. I've seen it do that, and I've seen it cause no issues. I had four 1st premolars pulled, so I can tell you in my case the face didn't sag. But I have great skin, and I had advancement that offset it a bit. You can also accept some space between the premolar and molars so as to not retract the teeth as much -- this is an option, too, but if the surgeon is Gunson he won't allow that and will want spaces closed. If the spaces are still wide enough, you can put implants in them as well. This is difficult but possible.