Cast iron waste drainage pipe has a life expectancy of about 50-70 years or so. Over time, the pipe may show signs of failure such as corrosive staining or corrosive scabs which are pin hole leaks that are scabbed over. Those scabs may not always leak, but it is often only a matter of time before they give way and leak into the home.
Aged cast iron pipes, or pipes that are showing signs of wear should be anticipated that replacement will soon be inevitable. Budgeting for the process can make the situation of plumbing replacement less stressful. Being proactive and having the portions of pipes replaced is a good idea as well.