Sometime this weekend, depending on when they hop into the private plane with the lips logo on the side to fly from Ontario to Washington, D.C., Keith Richards may sidle up to Mick Jagger and bring up an important issue: whether the Rolling Stones will play their cover of Don Covay’s “Mercy, Mercy” Wednesday at FedEx Field.

That may not seem like a big deal, unless you consider that, for the 3,198 times Jagger and Richards have played “Jumpin’ Jack Flash,” “Brown Sugar” and “(I Can’t Get No) Satisfaction,” Covay’s soul classic has been tabled — ever since the group’s free gig in London’s Hyde Park on July 5, 1969. (Their lone D.C. performance of the song came at the Washington Coliseum in 1965.)

“We’re working that up,” says Richards, speaking by phone from Canada on Friday. “The main thing is you haven’t played it for 50 years. So I’m just looking for the opportunity on the set-list to say to Mick, ‘Hey, today how about ‘Mercy’?”

It has been a slightly rough road to this date, the fourth of 17 on the second leg of the band’s No Filter Tour. Jagger’s heart surgery this spring pushed the concerts back from an April start, and also brought Richards a brief moment of contemplating a life without his compatriots — a reality, the 75-year-old says, “you kind of always know that could be coming.” But a series of Instagram posts made it clear that Jagger would be back, and he wouldn’t be gyrating from behind a walker. On June 21, at Chicago’s Soldier Field, the band — featuring core members Ron Wood and Richards on guitar and Charlie Watts on drums, as well as touring bassist Darryl Jones — played 20 songs, a concert bookended by “Street Fighting Man” and “Satisfaction.”

“As Ronnie and I often say to each other, let’s go onstage and get some peace and quiet,” Richards says.

There have been some changes over the years. Richards is off the hard stuff and, as the Daily Mail saw fit to print, he has ditched his bandanna and given his hair a slight brownish tint. But that doesn’t mean the onetime serial consumer heads to a Pilates class after soundcheck. He gets his exercise the way his heroes did: onstage.

“I have a beer occasionally, and that’s about it,” Richards says. “I live a normal life without being too preoccupied about my health. I find that what I do as a job actually is enough for me.”

He pauses and gives that Keef cackle, a laugh that falls somewhere between a pirate and a prep-school prankster.

“As you know, I’m different from a lot of people,” Richards says.

So is the band. The how-long-will-they-do-it narrative, birthed in the late ’80s, has given way to you-better-see-it-while-it’s-still-awfully-good. There is the Richards-Wood weave, with the guitarists swapping lead and rhythm roles by simply offering a look. There are the nightly surprises. Richards estimates the Stones worked up about 50 songs for the tour, meaning that “Sad Sad Sad” and “Monkey Man” were heard in Chicago. There is also an acoustic set part of the way through — the only real concession, according to Richards, to slowing down. That leads to the up-tempo stretch that closes out the show.

Without a record of new material to promote in more than a decade, a Stones gig remains steady and packed with staples, including “Honky Tonk Woman,” “Start Me Up” and “Sympathy for the Devil.”

Is there anything the band won’t play? Richards doesn’t hesitate.

“ ‘The Lantern,’ ” he says, referring to a forgettable cut on the band’s foray into psychedelic music: 1967’s “Their Satanic Majesties Request.”

It has been 14 years since “A Bigger Bang,” the last studio album of original songs. Richards says that in February, the Stones recorded at least five new songs with producer Don Was. They are likely to finish the album, which would be their 31st, later this year.

The Rolling Stones remain a kind of rock-and-roll chemistry experiment, an adventure to see how long it can last.

“Basically, yeah, nobody has taken it this far before, and there’s no guidelines,” says Richards. “And basically, we count on our audience. They’re incredibly loyal and you feel you would let those people down if you said, ‘I’ll chuck it in.’ ”

A week in, there also haven’t been any media-fueled blowups between Richards and Jagger. Though the guitarist has sniped at the singer in the past — in song, in his memoir and in interviews — this has never been Oasis. Richards says that their relationship has actually rarely been about conflict.

“First off, it ain’t like that,” he says of the supposed tension between himself and Jagger. “People only hear about the conflicts, which, after 50 years, there may have been two or three. The other 99.9 percent of the time, Mick and I are very close friends and have grown closer the older we get.”

He laughs.

“We are the only ones we know who are still alive.”