Residual Schizophrenia is described here: http://counsellingresource.com/distr...ia-description
Some of the new atypical antipsychotics claim to successfully treat the negative symptoms of Schizophrenia. ie they do not "worsen" the negative symptoms. They claim to have less side effects than the first generation of "typical" antipsychotics however side effects can include diabetes, weight gain and sexual dysfunction.
The relationship between depression and residual schizophrenia is an interesting one. It is believed that doctors often prescibe antidepressents for people they consider are depressed but who are actually residual schizophrenics.
The diagnosis seems to hinge on whether there is evidence of an initial actute phase of schizophrenia, ie one in which prominent positive symptoms appeared. In other words if you never had an initial positive-symptom "breakdown", it is unlikely that you have residual schizophrenia. Again, Doctors often optimistically interpret the intial phase as an acute depression and therefore the Schizophrenia diagnosis is missed.
Depression is a common factor in all phases of Schizophrenia and explains why so many comit suicide.