The CBS sitcom's seventh season concluded on Monday (May 14) with Robin (Cobie Smulders) being revealed as the mystery bride of Neil Patrick Harris's character.
Thomas hinted that the couple's wedding day in season eight - expected to be when Ted (Josh Radnor) meets the titular 'mother' - may not necessarily be saved for the finale.
"That wedding day is going to be full of enough other surprises," TV Line quotes him as saying. "There's going to be twists and turns built into that day.
"There's a lot of fans that think that's the end of the show - Ted meets the mother [at the wedding], and that's the finale.
"[But] there are people who think it could keep going, and there will be more story after [the wedding day]. What are Barney and Robin like married? What happens with that marriage?"
Thomas added that the next season will even see a new love interest for Robin introduced.
"It's not going to be Barney and Robin together immediately, because they're too tangled up in other things," he explained. "We'll show you how that relationship ends up leading her back to Barney."
Thomas previously revealed that the HIMYM team had planned for Barney and Robin to get married "literally years ago".
He also said that the show could very well continue for a ninth season.