How can we miss them if they won’t go away?

I was not thrilled to see “The X-Files’’ return last month for what Fox calls a 10th season and what I call an exercise in exhumation. The show isn’t burning out, as Neil Young might have it; it’s merely fading away. It’s not the “superb meteor’’ in a “magnificent glow’’ that Jack London spoke of; it has become his dreaded “sleepy and permanent planet.’’

In the late 1990s and early 2000s, “The X-Files’’ became one of those once-fine shows that just wouldn’t leave the air, even though it had been reduced to a pile of go-nowhere clues and failed promises. The series was a moneymaker and an integral part of the Fox brand, so it remained on the schedule. Its return this year, too, was not creatively driven. Like “The Office,’’ “Dexter,’’ “ER,’’ “Law & Order,’’ “Glee,’’ “House,’’ “Scrubs,’’ “Desperate Housewives,’’ “24,’’ “Entourage,’’ “Weeds,’’ “Frasier,’’ and “How I Met Your Mother’’ — and I could go on — “The X-Files’’ stayed much too long at the fair.

The reason I’m bringing this up is that three shows currently on the air have announced that they’ll be leaving — PBS’s “Downton Abbey’’ in March, CBS’s “The Good Wife’’ in May, and HBO’s “Girls’’ next year (after seasons five, which premieres Feb. 21, and six). All three shows could easily continue beyond those dates, as writers and cast members depart and fresh ideas become scarce. They could sail away into the sunset — in a dead calm — and make their networks happy.

Instead, they are preventing that kind of slow rot. They’ve all had their share of ups and downs of late, particularly “Downton,’’ but none has come close to a dreadfulness spiral. They will leave the air without a cloud hanging over them. Like “Breaking Bad,’’ “Mad Men,’’ “Friday Night Lights,’’ and many other shows, they’re dodging disgrace.

Right now, there are a few shows that should consider bidding farewell. When they finally leave, many former fans will be thinking “good riddance’’ instead of “miss you.’’ The most obvious over-stayer is “Grey’s Anatomy,’’ which is currently in the middle of its 12th season. Many of the original actors are gone, including the male lead, Patrick Dempsey’s Derek Shepherd, and the best character, Sandra Oh’s Cristina Yang. The writers are still squeezing the lemon, desperate to get another few drops of plot out of it; but where do you go after mass shootings and character deaths and dead character reappearances (Dead Denny, RIP-RIP)? You travel deep into Absurdity County, where you become a desperado with a keyboard and a pile of newspapers from which to rip headlines.

Other guests that are starting to smell like old fish? “Law & Order: Special Victims Unit’’ has been out of plots-of-the-week for years now, and efforts to pull the leads into story lines have bordered on comic. The show is in the middle of season 17. “Criminal Minds,’’ now in season 11, is another crime procedural that ought to consider a final exit. Shows such as “Law & Order: SVU’’ and “Criminal Minds’’ were never particularly original, as they followed network TV’s crime formulas. But still, they are now more like content factories than dramas.

Oh, and I’m not forgetting about you, “The Simpsons,’’ a beloved show that at this point — season 27 — is a shadow of its former self. Once a show that commented on pop culture while creating it, “The Simpsons’’ simply rolls along on old momentum. The writers remain smart and witty, there’s no question about that. But the relevance is gone, and the characters have been there and done that over and again. The fact that animated actors don’t have to age is one of this show’s great enablers. “Archer,’’ entering season seven on March 31, I’m looking at you, too.

Now in its seventh season, “Modern Family’’ still has a good episode every so often. But it’s uneven, and the characters repeat themselves to a degree that is no longer as dear as it once was. This is the time for the show to end, before it becomes fully used up. I can’t say a “Modern’’ departure would leave us wanting more at this point, since the show has passed that particular rubicon. But it would add points to the show’s legacy, saving it from becoming another TV barnacle like “The Office.’’

Jerry Seinfeld is something of a pioneer in this department. “Seinfeld’’ lasted a season or two longer than it should have, perhaps; but still, Seinfeld insisted on ending his series long, long before NBC wanted him to. When he announced his decision, “Seinfeld’’ was the country’s No. 1 show in the Nielsen ratings. The network threw all kinds of big numbers at him — reportedly $5 million per episode — but he resisted.

At the time, Seinfeld explained himself to The New York Times. “I wanted the end to be from a point of strength. I wanted the end to be graceful. We’ve all seen a million athletes where you say, ‘I wish they didn’t do those last two years.’ For me, this is all about timing. My life is all about timing. As a comedian, my sense of timing is everything.’’ To TV execs near and far: Put that on a plaque and read it.

Matthew Gilbert can be reached at gilbert@globe.com. Follow him on Twitter @MatthewGilbert.