How about to raise it late in the mission, to delay possible contamination?
In the mission plan, it was to be raised at the end of 2010 (end of the relay mission) but I haven't heard anything about that recently. If consumables are doing OK I expect that will be delayed as long as possible. They never did raise the orbit of MGS AFAIK.
Also, MRO's breakup analysis showed there were no planetary protection issues if it did crash; there was some sterilization to insure this (e.g., cable bundles.) http://adsabs.harvard.edu/abs/2008AdSpR..42.1108B