We present a mechanism of high-temperature sublimation of carbon nanotubes that does not destroy their ordered makeup even upon significant loss of mass. The atoms depart to the gas phase from the pentagon-heptagon dislocation cores, while the bond disruption is immediately repaired, and the 5|7 seamlessly propagate through the lattice. This explains a broad class of unsettled phenomena when at high temperature or under radiation the nanotubes do not become amorphous but rather shrink in size nearly flawlessly.