Except the rules
do warrant a deduction.
This is from 2016 rules (if anyone can find a more up-to-date link, please feel free to correct me), found on
this ISU.org page.
Rule 50
Clothing
1. At ISU Championships, the Olympic Winter Games and International Competitions, the clothing of the Competitors must be modest, dignified and appropriate for athletic competition – not garish or theatrical in design. Clothing may, however, reflect the character of the music chosen.
The clothing must not give the effect of excessive nudity inappropriate for the discipline.
Now, I am very liberal in my views & honestly don't care if nipples are shown on tv. But I do question if the nip slip warranted a deduction by this ISU rule. If it's against their rules, it deserves the deduction, same as if you had a piece of your costume fall onto the ice.