Cast iron pipe replacement for a SFH built in 1979

[Jason Sung]

For a SFH in Plano TX built in 1979 in recently purchased, it had foundation issue and plumbing issue. I fixed the foundation and now I am trying to fix the plumbing issue.

One bathroom in the living room is right on the spot with the foundation issue and it appears that it has not been used for long time. 

Would you recommend replacing the cast iron drain line since it lasts only 50 years? Or, should I just find the spots with issues and fix them? 

FYI, tThe house does not have cleanout and the cost estimate for installing cleanout is ~$1600.