Why didn't Roderick and Puck run off during Summer and Winter's discussion? As the quote from The Last Unicorn says, "never run from anything immortal. It attracts their attention."
Summer and Winter are actually Aspects. The power inherent in these two Queens is truly immortal. If a Queen’s body should die, their Aspect will choose a new body - usually the next most powerful - from her Court. The Queens will go to great lengths to avoid this as each body takes time to get used to the power and retains all the memories of the previous incarnation, including the dying.
It takes a great deal of power for a Fey to switch Courts. Very few have enough strength to do so.