Tallink-Silja Line offers day cruises (i.e. leaving Stockholm on the 13th, arriving in Tallinn on the 14th during the morning and leave on the 14th in the evening back to Stockholm) whose tickets are much cheaper than standard one-way tickets.
I've decided not to take the return leg of the day cruise from Stockholm to Tallinn and the line from Tallinn to Helsinki operated by Silja Line ferry, and the details of checkout information are helpful about not taking the return leg.
How do I do it? For instance, can I leave the cruise without any notification? Will cruise staff check whether I am back on board for the cruise from Tallinn to Helsinki?