People have been brought back repeatedly, even Zahn, after they were dead.
Zhaan reappeared as a voice in Stark's head and as a character in vitual reality video game created by Stark. I hardly count that as returning from the dead. Being in the science fiction or fantasy genres is not required for that kind of guest appearance by a dead character.
The only time that I can remember in Farscape when death wasn't permanent was Aeryn's in the S2 cliffhanger and S3 premiere. "Spare" copies of John, D'Argo, and Chiana were killed off after they were "twinned" in
Eat Me, and those "twins" all stayed dead. Rygel's apparent corpse in
A Human Reaction turned out to be a hologram. Aeryn's death in
The Locket ended up being an alternate timeline from everything else that we have seen since.
To be sure, the have plenty times when the audiance or the characters (or both) thought (for various lengths of time) that someone was dead, even though they had been alive the last time they had been seen. But in those cases it always turned out that they never died and there was some explanation, whether it was that Crais just lied about executing Xhalax or whatever. Again, that doesn't require SF or fantasy, although it does sometimes make the explanantions easier to swallow.
I think that TPTB at Farscape want to keep Aeryn's resurrection a special, singular event.
So the question returns to: "Do you think that it is possible that the characters actually avoided dieing?"
And I just think that D'Argo is the least likely to have not died. He is the one that I see the least reasonable explanantion for how they might have avoided death, and whose specific *death* was the biggest deal in the show that I think the writers are least like to want to mess with from a dramatic writing POV.
None of that has anything to do with seeing D'Argo in dreams, flashbacks, hallucinations, video games, bioloid replicant, or other such repsentations that are not the actual D'Argo.
EDIT: to add:
I just remembered Starks re-materialization. However, that was also a case where they just came out and told you in advance that Stark's Stacheri (sp?) nature might allow him to do that, so I tend to think about that differently.