How long can a person with pancreatic cancer be expected to live without surgery and only with chemo therapy ?

Depends: This really depends on the patient's given clinical situtation including the extent of their disease, other illness that he/she may already have, and their performance status (how well they can or can not do things on their own) but a rough estimate would be about a year.

Less than a year: Patients with metastatic cancer live generally less than 6 months without treatment and had a median survival of 11 months with an aggressive chemo regimen recently studied (folfirinox). Unfortunately, patients with locally advanced and even "resectable" disease who can not get resection usually do not fare better with chemotherapy alone despite having no evidence of spread initially.

Re-research: As dr bose correctly pointed out, most patients live only 11 months even with aggressive chemotherapy, and the so called targeted therapy tarceva (erlotinib) only adds survival by 12 days, and it costs (*000, 00) dollars. In my own lab, we found many "cheap" drugs probably more effective then the expensive ones, but again, we need more research to prove it. Funding....