What you do on your RTW is quite up to you. There are no rules to not fly home or take detours or whatever. OP is simply buying an additional product "Visit Pass" while in New York. I can't recall, but the two MAY actually have to be purchased at the same time as the RTW, since products like the visit pass often can only be purchased in conjunction with the internatiional flight bringing you to the country (to make sure that locals don't use it).