Go for it. If you perform very strongly on the MAT, your chances are certainly non-trivial, though I'm not sure if any more can be said. Maths in general has a pretty high offer rate elsewhere and unless your other options are like Durham, St. Andrews, Imperial, or etc. (the main ones I can think of that reject a substantial number of applicants) there's a pretty reasonable chance you will get most of your offers. Unless Warwick has changed its admissions policy in the last year, you would likely get an offer from them. Below this have a think about UCL, Edinburgh, Durham, Bristol, Bath, Lancaster, Birmingham and the like just to name a few good ones.