The sitcom will soon enter contract discussions with CBS execs for a ninth season, but the writers have begun the next run as if it may be their last.
"It's a really interesting situation because there's a negotiation going on that could extend the show, for sure," co-creator Craig Thomas told TVLine.
"But right now, the thing that we know to be true is we have this year and no deal for next year. So we have to proceed as though this could be the last year of HIMYM. Hopefully we will know soon.
"Basically, we couldn't possibly know soon enough. But we'd be thrilled to tell either story – either wrap it up this year or to tell another chapter of this story. We don't know yet which way it's going to go."
When asked if a possible ninth season would be its last, he added: "Who knows? We can't guarantee anything. It's not impossible it could go beyond Season 9."
The eighth season ended with a flash-forward (technically a flashback from Future Ted's storytelling) of Barney (Neil Patrick Harris) about to marry Robin (Cobie Smulders).
Talking about how they end up in that scenario, Thomas said: "They couldn't start further apart. Barney's engaged to another woman, and Robin is just getting into a relationship with [Michael Trucco's character]. It's fun. It's a fun challenge.
"We like painting ourselves into impossible corners on How I Met Your Mother. How do you get those two characters together? They're probably as far apart as they can possibly be. We will tell you that story. There's going to be some relationship carnage to free them up to do that.
"It's a bit of a relationship bloodbath in the first six episodes, and I hope in very entertaining way."
How I Met Your Mother will return for its eighth season premiere on Monday, September 24 on CBS.