The dynamic between Sam and Bucky was only seen briefly in Captain America: Civil War, but was a hit with fans nonetheless. That likely led to The Falcon and the Winter Soldier being developed in the first place with the two characters having a relationship akin to Mel Gibson and Danny Glover in Lethal Weapon.
After The Falcon and the Winter Soldier, there isn't much known about where Sam Wilson and Bucky Barnes will end up as characters. Obviously, this series is leading up to Sam Wilson claiming the shield once and for all as the new Captain America, but it's up in the air where Rogers' oldest friend will end up.
In an interview with John Nania on The Screen Forum podcast, Nania, Sebastian Stan's stuntman, talked about his career as a stunt performer and coordinator. When asked how much longer he would continue to do stunts, Nania mentioned how he wants to perform in front of the camera as long as he can before transitioning completely as a stunt coordinator:
"I've still got a lot of performing left in me, and there's still a lot of things I want to do. I don't think the Winter Soldier is quite over with in the Marvel universe, there's still a lot more to ride out on that one, and I look forward to being part of it."
John Nania seems to believe that he will continue as Sebastian Stan's stunt double for Bucky Barnes in a future project, but doesn't say more than that.
WHAT THIS MEANS
Obviously, something in The Falcon and the Winter Solider leads John Nania to believe that he could still be called back as Sebastian Stan's stunt double for the former Winter Soldier. It was rumored in June from Charles Murphy of Murphy's Multiverse that by the end of The Falcon and the Winter Soldier, Sam and Bucky "...are going to have gone through something traumatic and be different."
Additionally, if the show were to have a second season, "...it wouldn't be called The Falcon and the Winter Soldier Season 2, it would be a thematically related thing with a different name," according to Murphy. This indicates that the state that Bucky is left in by the end of this show will still leave the door open to his return. It's good to know at least that Bucky Barnes still has (hopefully) some sort of future in the Marvel Cinematic Universe.