Bands breaking up are always sad news, but after a long (enough) time, some say it's inevitable. Fans belive it's time certain bands wound up, as they can't play forever. Then there's Chicago. Yes, that's very far from a metal band, but we've seen a whole lot of lineups change gradually, but the band still soldiers on. One of the longest performing rock bands of all time seems to have a very effective succession plan in place, and a Golden Jubilee isn't out of reach. The Chicago of today is different from the Chicago that started off in 67, but they're still active, and going good. That's a little different from the Rolling Stones, who largely stayed the same for nearly five decades (three members didn't change)- but are older than Chicago, yet haven't broken up.
Can we expect any other band to do a Rolling Stones? or at least a Chicago? Maybe difficult with a metal band, as a long-running lineup will be very, very hard to emulate, so a new Judas Priest lineup will struggle to emulate the success of Halford-Downing-Tipton-Skull-Travis. I'd expect groups of the 1970s to last a lot longer than their later counterparts. Likewise, you won't find replacements for Klaus Meine or Matthias Jabs or Rudolf Schenker, so there may be no point in following a Scorpions lineup once they leave.
Iron Maiden is one band I'd expect to go the long haul, although they don't change much. They're still very fit and healthy, and much of the magic of old still remains. Saxon, not as famous as the Priest and the Maiden, can make it. Being a lesser name will help them a lot in carrying on further. While America's Riot is not so famous, they were formed in the 1970s, and are still going strong, but they've had their breakups in the middle. Accept is another very long-running band, but they've disbanded more than a few times, and it's anybody's guess when they'll break up again. Among those not so metal, Deep Purple (who broke up for a long time) and Journey can go the distance. Both bands have found adequate replacements for their illustrious band members who moved on. Aerosmith were likely to retire, but nothing has been confirmed. Rush have maintained a single, solitary lineup over time, and haven't retired, but they don't record so much these days. Surely the Canadian trio may do the Rolling Stones?