Alternative sewer line in basement
I think that is a viable idea.  I know that the cast iron pipe can present some serious issues, cracking, collapsing, etc. Quality control in manufacturing of pipe has improved dramatically over the years.  That old cast iron pipe had thin spots.  Also, I would be concerned about the original grade as in pipe slope; was it proper and or adequate.  If I had two serious clogs in a relatively short period in a metal pipe nearly 100-years old,  I would surely be looking for a better solutions than to call the rooter man again. Use a pump for the basement sink. Good Luck. P.