I'm not sure why the cone becomes seperated from the housing, but mine was OK when the impeller split in half. Maybe the cause was corrosion related from infrequent coolant changes. Perhaps some kind of impact occured from a disintegrating impeller.
Whatever the case, a new housing/cone would be the best but most costly option. I would recommend a thorough inspection of the cone and base your decision on that. If there are any signs that it is coming loose, by all means replace the assembly.
IIRC, someone in CEG used epoxy to secure the piece to the housing.
