Answer from cs61c-ck (Allen Lee 16583554) for Question 4
No, just like how the nodes of a circularly linked list might remain after a reference counting garbage collector, this structure remains after garbage collection because each "object" has a non-zero number of pointers to it.

However, since this structure appears to be unreachable, the garbage collector will not mark it during the mark phase and thus gets reclaimed during the sweep.