Understandable on your part for sure! I am assuming IF the spring content is free some things (e.g increased light level) will require TTK so hopefully it works out for you. Also if you haven't been already I'd keep an eye out for sales of the physical version of Destiny that comes with TTK. Amazon is currently selling it for 39.99 which is the same price as the DLC alone but I'm willing to bet it will go on sale at some point. Maybe that would entice your mates to make the journey back!