You can't design out the MRGB but maybe you can reduce the effects of a failure.
Look at how the gearbox works in the 500 and I believe the Apache.
Most gearboxes support the main rotor and have flying controls bolted to them. A major failure can lead to loss of rotor and/or control.
In the 500 design the gearbox is underslung and in theory could fall out completely with no effect on the flying controls and the abilty of the aircraft to autorotate.
For large aircraft this would be a radical redesign, resulting in either less internal space or a taller aircraft. Not impossible though just different.