Before points are deleted, all primitives referencing the points will be notified using dereferencePoint or dereferencePoints. These methods should return the appropriate DeferefenceStatus.

A quadric primitive will return

GA_DEREFERENCE_OK
If it's point is not in the point group
GA_DEREFERENCE_DESTROY
If it destroyed its vertex A hull primitive will return
GA_DEREFERENCE_OK
If a full row or column was dereferenced
GA_DEREFERENCE_DEGENERATE
If a full row/column was dereferenced, leaving a degenerate primitive.
GA_DEREFERENCE_FAIL
If a single point from within the hull cannot be dereferenced The dry_run parameter will prevent the point from actually being detached.