The CBS sitcom's next run will pick up where last night's season finale ended, with Robin (Cobie Smulders) revealed as Barney's future bride.
"We ended the season finale with a lot of, for lack of a better term, mind-f**ks," Thomas told Vulture. "So we'll have to do a whole episode stuck in that time frame. And then in episode 802, we jump ahead... and catch up with everyone."
It is currently unclear if season eight of How I Met Your Mother will be the show's final run, Thomas added.
"We're already breaking stories [for season eight] now, and it's tough not knowing if we're writing one or two more seasons," he admitted. "It will affect what we're doing next year. So the hardest part is not quite knowing."
The show exec insisted that he would be happy for the comedy to conclude either in 2013 or the following year.
"I won't say whether we're leaning one way or the other," he said. "When we were launching the show, we always thought eight seasons would be great for what we were trying to do. So eight would be awesome.
"But we just came off our best ratings year. We still think we have great stories to tell. I don't know - it's hard to say goodbye."
Cobie Smulders recently suggested that How I Met Your Mother would indeed conclude next season.