I'm glad I asked for clarification, as my research had indeed gone in
the direction opposite of what you were looking for.
Sadly, the answer is that usually yes, when one conjoined twin dies,
the other follows shortly after:
"The tragedy for conjoined twins who spend their lives together is
that they inevitably die together too. When one twin dies, the heart
of the other twin keeps pumping until he or she is drained of blood."
"All conjoined twins depend on each other for life. Their blood flows
between them as one system. When one twin dies, the other dies soon
after, unless separated."
"Some operations to separate conjoined twins have proven successful.
Such surgery is very delicate since the twins share blood supply and
Case Studies of Conjoined Twins
Not all conjoined twins share circulatory systems:
"Conjoined twins may be attached only by a cord of tissue, or they may
be fused at some part of the body, such as the head, chest, or leg.
Sometimes they share one or more internal organs, such as the heart or
liver, or they may have a common circulatory system. Surgical
separation of conjoined twins has been successful, although if the
twins share important organs, surgery may be risky for one or both
...but those who do not are typically separated. It's more common for
conjoined twins to share a common circulatory system and heart (35% of
conjoined twins are thoracopagus - joined at the thorax.)
Select Types of Conjoined Twins from the top bar, then Thoracopagus
For more information about conjoined twins:
Conjoined Twins at DMOZ
Conjoined Twins at Yahoo Directory
I hope this answers your question! Happy Solstice!
Search terms: [ "conjoined twins" ], [ "conjoined twins" survival ],
[ "conjoined twins" one dies ]