If I have a DONE4 and have ticketed it with say side trips in NA or Eu, and then mid trip by the time I get to those segments I decide not to travel them (eg. due to time constraints) can I just not travel them and keep going on the next segment I want to or will the relevant airline mark me as a no show and cancel the rest of my ticket?

Eg. - MEL-LAX-LHR-FCO-LHR-RIX-LHR-MEL but instead I just want to go MEL-LAX-LHR-MEL