I haven't read the whole thread, but wanted to say your poor ds. 
If it were me and one of my ds, I would be looking at moving him to another school, as any school that is happy to leave a child in that state, is not one I would trust with my child's care day in day out.
I do understand that teachers have their hands full and can't leave a class to clean up a child, but surely there must be someone available to help in these situations, which are a fairly regular occurrence in a lot of Reception classes.
Diagnosis has absolutely nothing to do with it, its basic care that's the issue, along with consideration of respect and self-esteem for your ds. If a diagnosis and treatment plan is forthcoming thats all to the good obviously, but as you quite rightly state, this situation cannot be allowed to continue in the meantime.
How far have you gone with regards to your complaint? To get something done, you would most likely need to complain in writing, to the teacher first and formost, then her line manager (Head of Year or Head of Infants depending on the school) then the Head of the School and if still nothing is done your complaint should be escalated to the Governors and then the LEA.
In the first instance, I would write formally to the teacher, detailing exactly what the issue is and asking for a written response and plan of action. If it were me, I wouldn't wait to take it any further throught the complaints process, I would write again, to the Head, stating that you are taking him out of school to homeschool until a more suitable placement can be found a different school.