This question already has an answer here:
For example, Air France offer some tickets that combine flight and train to the final destination. After I arrive at CDG, if I don't take the train to the final destination, are they able to see whether or not I took the SNCF train?
If they can see it, will they cancel the return tickets for train and flight? It is important for me to understand this.
And if they really check, can I go to the train station, and then just leave the station? It's hard to believe they check whether I went to the final destination, right? I hope someone knows how this works.