That is a tough one. I can see why that would be a real challenge and a real source of frustration for a parent in the context of a mass. I typed up a long post and wound up deleting it, because I don't want to pretend I know a lot about a situation I haven't really experienced from your side of things, and I didn't want to get too deep into some of my own personal information that might or might not be relevant (I've made the mistake from time to time of going too in-depth about personal things and then had to deal with a long frustrating Internet debate about things I don't really like to talk about in the first place, that I get really upset over -- so I'm attempting to do less of that.
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In a nutshell, though, my knee-jerk reaction would be to say the first thing you should do is find out if your child wants to go to mass or not. If the child can't help misbehaving because of his disabilities but really wants to be there, that's a good reason to try to keep at it and work through stuff. If the child really doesn't want to go, it might be worth considering leaving the child at home.
A child with autism is not a typical child who can be coerced into doing something smoothly -- often if autistic children don't want to do something, it'd be easier to move heaven and earth than to make them do it. And sometimes autistics have good reason for wanting or not wanting to do things that it's hard for regular folks to understand, because the two groups have very different ways of thinking. So giving your child the benefit of a doubt that he might be clued into something about himself that you aren't that he can't quite express in a way you'd be able to identify with, especially if he is older and a higher-functioning autistic, could be a worthwhile idea to think about.