Cash In Meaning

(idiomatic) To die.

Example:   Lots of people tried to cash in on that market, but few succeeded.
1907, Robert Service, “The Cremation of Sam McGee”, in The Spell of The Yukon and Other Verses:
  He turned to me, and "Cap," says he, "I'll cash in this trip, I guess; / And if I do, I'm asking that you won't refuse my last request." ¶ Well, he seemed so low that I couldn't say no; then he says with a sort of moan: / "It's the cursed cold, and it's got right hold till I'm chilled clean through to the bone. / Yet 'tain't being dead — it's my awful dread of the icy grave that pains; / So I want you to swear that, foul or fair, you'll cremate my last remains."