“More times than I can remember, a spouse or child has said to me, ‘If he wasn’t dead, I’d kill him all over again for leaving me with this mess,’” said Greg Rohan, the president of Heritage Auctions.

Most people tend to know what to do with traditional investments after someone dies, he said, but when it comes to baseball cards, first-edition books, coins and other collectibles, the loved ones dealing with the estate can be stumped (and annoyed).

If some collectors of, say, vinyl figurines, seem to have a gene that spurs them to dedicate entire rooms of their home to inanimate rubbery friends, they are also, in many ways, just like everyone else. “People don’t want to think about dying,” said Maggie Thompson, 80, a former senior editor of Comic Buyer’s Guide, which was a newsmagazine that covered the comic book industry. “I realize as I look around my rooms, my family is not going to know what things are.”

Ms. Thompson, whose eclectic collection includes Polaroid photos, film posters and comic book art, knows firsthand that not having a plan can mean a lot of responsibility for survivors. Her brother, Paul Edgar Curtis, died last year, and her family spent months dealing with his comic books and other mementos.

The market for many collectibles has been heated of late. In April, a rare Pokémon card sold for $300,000 at Heritage Auctions. Last year, the original art for a comic book page featuring Spider-Man in his black costume sold for $3.36 million at Heritage, and a copy of Superman No. 1 went for $5.3 million in a private sale. In 2021, a Nintendo Mario 64 game in its original packaging sold for $1.5 million.

Those rarities — and their enriched owners — aside, collectors can have a disconnect from their families. “I’m not going home and talking to my partner or to my kids about what I collect because nine times out of 10, they don’t care,” said Josh Benesh, 38, the chief strategy officer and general counsel for Heritage Auctions. (His own collectibles include television and film props, American regional art and modernist jewelry.)

Many collectors keep a mental log of their wares, but they would be wise to keep a physical list and address their collections in their wills. “It’s not really about doing it for the sake of money, but it’s making sure that the responsible stewardship of your collection extends beyond your life,” Mr. Benesh said.

Karl Heitmueller Jr., 58, runs The Daily Superman on Instagram, where he highlights his Man of Steel memorabilia. He has grappled often with the fate of his collection. “All the people to whom I plan on passing on my collections are close to my age,” he said. “So it’s a crapshoot. Who is going to kick first?”

Mr. Heitmueller said that his brother, who has collected more than 10,000 vinyl records, would be the primary beneficiary, with other items earmarked for friends. “It’s one of those things I need to work on,” he said. “If he were to die first, I wouldn’t know which of his things were worth a lot of money and vice versa.”

Still, Mr. Heitmueller has a vision of what he’d like to see after his demise. “I don’t want a funeral,” he said. “I don’t want a memorial service. I don’t want money wasted on any of that stuff.”

Instead, he would like his family and friends to browse his collection and take what they want. “If I were to die tomorrow, I would like to think that all of them would not mind having a Superman action figure of mine to keep to remember me by,” he said.

Richard Pini and Wendy Pini, whose comic book fantasy series ElfQuest debuted in 1978, wrestled with what to do with her body of work for most of their professional lives.

Over the years, they had amassed thousands of pages, including all the original art for the series, which was written by Mr. Pini, 73, and drawn by Ms. Pini, 72. “He would never envision selling off the work individually,” Ms. Pini said.

Mr. Pini said it would have been heartbreaking to sell it piecemeal. “I saw lines being put down.” he said. “I heard the curses when she needed to reach for the whiteout. It was all very personal.”

Selling the artwork could have been lucrative. “There are art dealers who come up to Richard at conventions,” Ms. Pini said. “They’ve never even met him before, and the first thing they say is, ‘You idiot. You could have made millions off of selling the artwork.’”

Mr. Pini said that they knew they wouldn’t be leaving their collections to their families, who weren’t particularly interested in ElfQuest in the first place. The fear, then, was that the material would end up at a garage sale.

Their knight in shining armor came in the form of Karen L. Green, the curator for comics and cartoons at Columbia University, which acquired the Pinis’ work in 2013. “We treasured the idea of students and fans studying it in the future after we’re long gone,” Ms. Pini said.

But many collections are destined for less hallowed institutions. When the end comes, families sometimes go to the most convenient source — a local comic book store, a pawnshop — and may only get a fraction of what their collections are worth. In other cases, a collection is worth much less than what the owner, or inheritor, thought.

Vincent Zurzolo, an owner of Metropolis Collectibles and ComicConnect, recalled a story from early in his career. A man thought he had a hugely valuable set of stamps, he said, and “my employer went down to look at the collection and it turned out all he did was cut out pictures of stamps and put them into a book.”

Still, it’s hard to predict the value of collectibles, given that not long ago a first-generation iPhone fetched $63,356.40. Collectors — and their families — would be wise to remember the marketplace can be fickle. “Collectibles do go down in value,” Mr. Benesh said. “We don’t like to talk about that, but there are Beanie Babies in this world.”