I looked at the transcript Lostpedia had out, and most of what Dogen says has the Japanese and english translation. This particular line only had the Japanese so that is what my friend looked at. However, I can't be completely sure that that is what Dogen actually said since it's someone else's interpretation of Dogen's line. I'd think "to pass away" would be easy enough for Lennon to translate, so you are probably right that it is some sort of slang they use to be somewhere between "pass away" and "claimed."