Waiting for the Big One: A New Class of SGR Outbursts?
  It is suggested that magnetars eventually become unstable to a dynamic overturning instability that destroys most of their dipole moment in a single event. It is further suggested that such an instability would produce a supergiant version of the largest soft gamma ray bursts that have thus far been observed, and that they could be observed out to tens or even $10^2$ Mpc. Persistent emission and afterglows from the fireball might confirm positive identification with nearby galaxies and perhaps provide other distinguishing features as well. 
David Eichler