Weirdly, this is such an unrealistic scenario that I'm having trouble coming up with something spectacular. It assumes that not only am I free, but my players are free too, which is even less likely.
Ideally this would translate to a group of friends staying somewhere away from it all like a cabin on a lake with the goal of playing for a week straight. I'd like at least 3 of us to have prepared campaigns just for this week. Maybe two of them are RPG's and the third is a miniatures campaign or a boardgame tournament of some kind to change things up.
I get I am focusing on the setup here more than the actual game - so what would I actually do?
- One attractive option would be to run a big D&D adventure. My initial thinking is "Temple of Elemental Evil in one go!" - that would be a lot of fun and a strong way to kickoff a new campaign. At a higher level, running the whole Giants series one right after another would be fun too. Running one of these big scenarios all the way through with the same group of players in the space of a week would be a blast.
- The big Star Wars adventure: A new group gathers, maybe new characters with a smattering of returning favorites, a new mission/problem beckons, and resolving that is the first part of a "trilogy" of adventures played out over the week. Finish one, take a break in between, then start the next one. This could be a set of stories running parallel to the movies or it could be completely original and set in say the Old Republic. Come out of the week with an epic adventure completed and some fun stories to tell.
- Star Trek Reboot: Something a little similar to the 2009 Trek reboot - a new crew gathers on a new ship for a simple shakedown cruise and then events spiral out of control and the PC's are caught up in an epic Trek story that could be the foundation for an entirely new campaign. The "bonding" that happens running a set group of characters through a bunch of table time in a short period like this would be a really nice setup for a new campaign start. This would involve Klingons and/or Romulans, maybe time travel, some new aliens, a threat to the Federation, and at least one bar fight. This is a "movie" adventure, not a "one episode of a TV series" adventure so ships might not make it, characters might not make it, and a lot of standard assumptions about Trek status quo are on the line.
- Invasion! A 6-issue limited series: A superhero campaign based off of an alien or dimensional invasion. Ideally this would be a special game that takes place in a campaign that is already up and running. Instead of dealing with bank robbers or one mad scientist or some "hunteds" this would be an epic story that would see familiar NPCs and institutions and possibly the very home setting of the game threatened with occupation or destruction by a new menace. Of course, some old menaces would likely ally with this new force, but some old menaces might instead team up with the PC's to help fight it off. Tying it to an ongoing superhero campaign makes the people and the places that much more important when they are threatened. The events of this special mini series would at least "leave a mark" on the ongoing campaign. Characters and NPCs might fall, tragedy and/or heroism could affect the city and the people who live there, and some destroyed landmarks might never be rebuilt, instead becoming a park with memorials to the events and casualties of the invasion.
- A Savage Worlds plot point campaign: There are a fair number of these and I think it would be entirely possible to run them in the course of a week mixed in with other games: Necessary Evil, 50 Fathoms, Evernight, one of the Deadlands plot points, Slipstream, Tour of Darkness - all of them are cool and depending on the group and the general mood I know I could pick one and run a rollicking good game in the course of a week .
So all of these represent an opportunity to me to either kick off a new campaign in spectacular fashion, or to celebrate an ongoing campaign with an epic special run that affects the ongoing game. Either way it should be somewhat self-contained so that someone new could join in and make a meaningful contribution, or so that even if you never played another session you had a complete run that made some kind of interesting story to tell later. Also note I am not really tied to any particular edition or version of a game - just whatever makes the most sense for that group at that time.
I don't think it will ever happen but I think it would be a ton of fun.