I'd be recording all the conversations in writing so you have a record as its amazing how people deny saying things like 'no m/s school will take him' when you ask for a more expensive SS.
So write back 'i just want to confirm our conversation on...' and send it to them. It then stands as a record unless they write back and correct it.
You should look at the PRU so if it does end up in a tribunal situation you can show you have been reasonable and considered all the options
You can ask the PRU what behavioural training for children with autism the staff have and how they intend to work on your child's behaviour and how they intend to generalise that back into mainstream. Ask them what success they have had in the past in similar cases. If the answers are none - and there is no peer group - that strengthens your case for refusing.
I agree a permanent exclusion is useful in terms of getting better provision. You can appeal the exclusion if you want (although you may not want to go back) see info here You can now get an SEN expert involved in an appeal against exclusion and this person has to be independent of the LA.
You sound like you would have a good case for appeal as the School has not made reasonable adjustments or put in SEN strategies. Poss also disability discrimination. But this school sounds awful and I know children who have stayed in schools like this and had a mental breakdown by 9/10 because of how they are treated
You need to find the right solution for your child and put your efforts into getting that on a statement. Which means looking at all the schooling options eg ASD units, indep special schools, ABA etc
My DS is in a mainstream school with ABA support and that works well. But I recognise it would not work without ABA - as school staff don't know enough about behaviour / autism.
The school are supporting another boy who does not yet have a statement with FT untrained TA 1:1 - while they are trying this boy has made no progress in 2 years because the staff still can't get him to sit down and follow a 1 step instruction. The SLT and autism outreach here are useless and know nothing about behavioural approaches. So even in a willing school if the expertise is not there then its not the right solution.
So I would look at SS, units, ABA etc and work hard to get that. It doesn't mean he can't go back into mainstream, just he's not ready yet and the school is not skilled enough.
I wouldn't ''pull him out" as if you home ed you take over financial responsibility and they don't need to do a statement if you are providing an adequate education. You can refuse for him to go to PRU and if HT refuses to have him back then the LA must find another school and provide home tuition in the meantime. There is a legal difference to a child being educated 'otherwise than in school' which is an educational placement itself and a child being home educated. You want 'education otherwise' eg home tutor / home programme funded by LA or school until an appropriate placement is found
I would get IPSEA or NAS etc onboard as you can be allocated a caseworker who can help you.