WHAT SHOULD YOU DO?
I thought about responding to this with an email, but I decided to try a response in substack instead. I loved your ideas for dealing with dwindling enthusiasm for a campaign and have used them or slight variations in the past. My primary game is an AD&D game that I play during lunch at work. I currently have 4 players (2 originals and 2 who joined later), about a dozen other players have come and gone through the campaign, with a per session high of 9 and a year or so where I ran two concurrent games with 4-5 players each.
Hitting pause has worked for me in the past, but I try to make it a fixed scope - "We're going to take a month off and play this other game."
Introducing a new wrinkle into the campaign is also a good move. In a small twist on this, I've run short arcs in the campaign where we moved away from the main group. Sometimes that's meant a quest for a group of retainers. At other times it's been solo adventures, or small group adventures for a subset of the PCs - "While the magic user is holed up in the library at Hafen doing research, the druid and the ranger want to check out rumors of a treasure hunter who's gone missing on the coast."
Asking players to get their perspective is also a nice option. My favorite was holding a 2 year anniversary session where I prepped a bunch of questions on index cards that we flipped through and answered while eating pizza together. We reminisced about things that had happened in the campaign to that point and dug into some inter-character relationships.
I also like to ask questions during play, "What do you see about the door that makes you think the other denizens of this area fear whatever is behind it. I find that engaging my players in a bit of world building takes some of the load off me and gives me some fun threads to tug on as the game progresses.
I'm looking forward to hearing/reading what other folks have to say, dwindling enthusiasm can be a campaign killer if not dealt with.
These ideas focused on the DM side of the table, I also worry about what happens when the players lose steam. Any thoughts for what a player can do to stay connected and interested in a long running campaign?