Once your Premium subscription ends, your viewing access will change to the free version.
You'll still be able to watch the first themed compilation you viewed while covered by Premium as many times as you like as long as it remains in the lineup. Other themed compilations will have lock icons. These compilations will not be viewable even if you could watch them while subscribed.
After the themed compilation available for free disappears from the lineup, the compilation at the top will become available for free.