The dmf is there primarily to damp idle rattle and improve low rpm refinement. Removing it will remove this damping effect so you can expect more idle rattle and so on. It won't kill your gearbox!. The torque required to compress the dmf springs is very low - they are acting as the interconnect to the 2nd part of the flywheel to smooth the engine angular accelerations due to the crank oscillation, which is a function of engine balance, inertia and ancillary drive loading etc. This damping is required most at low torque (eg idle) when you only have gearbox drag torque to deal with. There are plenty of old diesels out there with no dmf that have done high miles, though theres probablt a bit of gearbox clatter and rattle if you listen. When the time comes I won't hesitate to junk my dmf.