Bellamy’s fate was left ambiguous at the end of The 100 season 7, episode 5, "Welcome to Bardo", but he likely survived by traveling through the Anomaly. Bellamy’s whereabouts and whether or not he was alive has been a driving force in the final season after he went missing early in the season 7 premiere.
Bellamy’s absence is slightly awkward for the show, as he’s been a central character since the series began in 2014. When the actor, Bob Morley, requested some time off from the show, he was written off as being kidnapped by the people of Bardo, starting the plot down the direction of exploring the other habitable planets connected to the Eligius III mission.
After a few weeks ago, Bellamy finally made an appearance in The 100 season 7, episode 5 next to the Anomaly Stone on Bardo, trying to free his sister, Octavia. His appearance ends in a cliffhanger, as one of the Bardo soldiers sets off some sort of grenade. After the blast, Bellamy disappeared and the Anomaly closed, raising the question of what happened to him. Echo and Octavia each react as if Bellamy was killed, but that’s probably not what happened. Instead, he likely traveled to one of the Anomaly stone's other planets.
Before Bellamy disappears, the Anomaly was opened behind him. While it was a mystery in The 100 season 6, season 7 has explored the Anomaly’s nature as a wormhole, acting as a bridge between worlds across the galaxy. After noticing the soldier reaching for the grenade, which seemed to create a flash of light more than a large explosion, Octavia yelled for Bellamy to jump back through “the bridge”, as many characters call the Anomaly. While the light blinded the characters and the camera, Bellamy could have jumped or fallen back into the Anomaly to escape.
Since Bellamy hasn’t been seen on Sanctum in quite some time, this would most likely put him on another planet, possibly Nakara (where Clarke and some others are currently stranded) or on Etherea, which hasn’t yet been seen outside of the opening credits. This allows Bellamy to have survived the end of “Welcome to Bardo”, gives more reason for the series to explore new planets, and gives the actor additional time off from the show.
It's unlikely Bellamy is dead, as it wouldn't make sense to kill him off in such an anti-climactic way. Bellamy hasn’t only been on the show since the first episode but is also one of the fandom’s most beloved characters. The 100 has never been afraid to kill off beloved characters, but those deaths have always had weight. This scene wasn’t given nearly as much weight as those, making it likely he survived in some way and made it to a new planet.