No, the general consensus is that prophylactic mastectomy should be done just as it would be if the mastectomy was for treatment of an active cancer in the breast with respect to clearance of breast tissue. The goal is to remove 98% or so of the breast tissue and not leave behind tissue that is visible to the naked eye. This means that small bits of breast tissue may remain but all possible is removed to achieve the goal of significant risk reduction. This is known as a "skin sparing mastectomy" to differentiate it from a "subcutaneous mastectomy". Sometimes the terms are used interchangeably and so care must be taken to understand what your practitioner means when they use one or the other term. Nipple sparing mastectomy can and is done when indicated along with skin sparing technique but doesn't purposely leave a "carpet" of breast tissue behind under the skin. This may increase the risk of healing in the preserved nipple area but with careful technique the nipple typically heals just fine.
The only subcutaneous tissue that should be left is the subcutaneous fat (doesn't contain breast tissue) that is between the breast tissue and the dermis of the skin.
Hope this helps,