Complex sentence: According to the expanded universe, 9 years after his encounter with the Wampa, Luke returned to Hoth and encountered the very same Wampa whose arm he had severed and the Wampa, in turn, remembered him and his lightsaber due to their long memory spans.
Split into simpler sentences: According to the expanded universe, Luke returned to Hoth nine years later and encountered the very same Wampa whose arm he had severed. The Wampa, in turn, remembered him and his lightsaber due to their long memory spans.