After Drake died with Riot in Venom, the symbiotes were still in Drake's lab. So what happened to them? Are they disposed or sent back to space?
In the beginning of the movie, there are a total of four symbiotes. One escaped in the crash and hopped from one host to another. The other three were taken to the lab.
It is explained earlier in the movie in a one-off sentence that symbiotes need a host to live in an oxygen rich environment. The symbiotes also killed their hosts if they weren't compatible matches, so Carlton Drake's solution was to just keep sending in "volunteers" in hopes that one of them becomes a stable match.
Eddie Brock escaped the lab while bonded with a symbiote. Drake evidently ran out of hosts as there are two quick scenes that show dead symbiotes. Drake also explains to Riot that he tried his best to keep them alive.
There are four symbiotes total on Earth. Riot continually bonded with hosts until he found Drake. Venom bonded with Eddie. The other two unnamed ones are dead because they were unable to find a suitable host.
I believe we see that the two other symbiotes are dead, either because they couldn't find a suitable host or the host died. One dead one is seen when they are talking about running out of test subjects and other one is seen dead when the doctor killed herself.
Carnage's Host is shown in the post credit scene, teasing a second venom Movie. Thus meaning the Red symbiot survived.