When a parent CI is retired, the related child CIs (both hardware and software CI’s) do not automatically get retired.
- Login to any out-of-the-box instance
- Open 'cmdb_rel_ci' table
- Open both Parent CI as well as one of its Child CI
- Change the 'Install status' of the Parent CI to 'retired' and see that it does not change the 'Install Status' its Child CI.
This is out-of-the-box behavior of SeviceNow Instance. Please create an enhancement request should you wish to see it in future releases of ServiceNow.