Yes Sue is there, I believe she is outside just before you go into the building, but I could be wrong on that it has been so long (I have only actually seen her all together once...I am used to her being in the lab where they were puting her together.
As for your other question... Dinosaur is very easy to get out of if you don't want to ride. The rotunda,main que, is where the Dinosaurs and little exhibts are (with narration from Bill Nye the Science Guy). Once you go through the Rotunda is the pre-show video, once the doors open from the pre-show your wife and son can exit from the double doors on the far left end of the hallway, those doors lead to the exit area of the ride (where you will come exit), depending on how long the que is from the pre-show to the ride vehicle it should take you about 10-15 minutes (or less) to get through while they wait (there is a gift area there as well as the ride photos). If they choose they can also wait the entire line with you and just walk through the vehicle when you get on (you get on and off at the same place), they would need to continue through to the exit as they can't wait right there, but then they would only be away from you for the few minutes that the ride actually takes. If you want to do the child swap, and you use this option just let the CM loading the vehicles know and they will advise you what you need to do. If you choose to have them wait at the exit right after the pre-show, the child swap is done from the outside exit area, just find a CM and advise them that you waited the ride together and your child didn't want to go and they will direct you.