Two things here;
Firstly, Warwick Road will be crawling with OB, so apart from planning on getting their arse bitten by a police dog, batoned to th ground by T.A.G and being trodden under the hooves of Champion the Police Horse, can't see that their 'plan' will amount to much.
Secondly, whilst it's possible that one or two stragglers might get picked off, my experience of Utd, as with most football 'firms', is that when faced with anything like equal numbers, they're not really interested. They may jump about a bit and make a bit of noise, but a proper kick off is very, very unlikely.
My advice to anyone, red or blue tomorrow night, is if you're on your own, don't flaunt colours about and if possible, go mobbed up.