What are the characters up to in the 80s?

They all die of lung cancer.

Roger would be unlikely to make it to the 80s.

I guess Don would live another decade or two and as the OP suggests, work on the biggest accounts before collapsing of a heart attack in his early 60s.

Peggy is a successful ad agent with a string of failed romances behind her.

Pete makes a living earning big bucks and then blowing it all. Assuming he manages not to kill someone in a desperate rage, he is still an agent, works on big accounts but never makes it to the very top.

Joan is an Oscar-winning film producer.

Sally is a vegan health freak who, after Betty’s death, devotes herself to trying to force her dad to mend his ways. Unsuccessfully, of course. They have frequent, lengthy fall-outs over the last years of his life, but his deathbed reconciliation with her would make one of the best lump in throat TV scenes ever...

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What are the characters up to in the 80s?

Coke. Talking here the sort that was all over Miami during the decade in question, and not the company that Draper put out an ad for in the final episode of the series

Yes, Don dies of a heart attack in his sixties. He's still in advertising up to the end but has lost some of his luster, he'd had to take any job to pay for all the divorces, and everyone knows it.

Sally becomes the antithesis of everything her mother was, and ends up a lesbian professor of history at a liberal arts college, with frizzy hair and a natural-fiber wardrobe. She loathes the 1980s, Reagan, yuppies, and advertising.

Joan becomes a successful TV producer, and is behind some of the middlebrow daytime talk shows, among other projects. Gave Oprah Winfrey a bit of help breaking nationally, and Oprah is always glad to do Joan a favor.

Peggy becomes a partner at a new firm, is rich, but gets stuck with the administration because she's still regarded as uncool in the industry.

Megan's current husband is a corrupt governor, she's the perfect polished political wife, and never stops gathering blackmail material to use in the divorce. She always does.

The circumstances of Roger Sterling's death have never been made public.

Don - he achieves all he set out to achieve on Madison Ave, then moves to California to open his own boutique ad agency. He finds love again but doesn’t marry. The smoking and drinking take their toll and he dies in his mid 60s.

Peggy - becomes a trailblazer for women in the ad business. I think she and Stan make a go of it and have a good life together. They have two sons and raise them in the city. They renovate Peggy’s building, creating a design studio for Stan so he can do freelance work at home.

Joan is also successful in producing corporate films. Her son grows up and joins her. He uses his inheritance from Roger to expand the firm into producing A list Hollywood movies. They jointly accept an Ocsar in the late 1990s. Joan recruits Sally as an intern then director who goes on to direct indie films. Her first film is about Vietnam vets which she dedicates to the memory of Glenn.

Roger’s health deteriorates in the 1970s. He makes peace with his daughter and dies alone at a villa in the south of France while Marie was off seducing a younger French man.

After her acting prospects fade, Megan returns to writing. She regrets giving up the ad business after taking her early copy writing accomplishments for granted. She becomes a tv script writer, works on scripts for ‘80s night soaps Knotts Landing and Flamingo Row.