Wouldn't it suffice to do a coreference pass before extracting sentences? Obviously you'll compound coref errors with the errors in your main logic, but that seems somewhat unavoidable.
I am working on this in my kbsportal.com NLP demo. With accurate coreference substitutions (eg., substituting a previous NP like 'San Francisco' for 'there' in a later sentence, substituting full previously mentioned names for pronouns, etc.) extractive summarization should provide better results, and my intuition is that this preprocessing should help abstractive summarization also.