There is still Hope for Season 4
Carlos Coto, the showrunner of From Dusk Till Dawn seems hopeful.
When the news first broke out about the cast being released & thus the possibility of show not getting picked up for another season, he wrote on Twitter:
"All I can say is we all know damn well how hard @DuskElRey characters are to kill #nothingelsetosay #FromDuskTillDawn"
Then after the S3 finale yesterday, when someone asked him if he could tell us how much time passed between the last battle and the last shot of the episode, he refused to answer saying that he cannot give anything away because he'd be spoiling it.
Some fan asked him then if this means there's still hope for Season 4. He responded with "There's always hope!"
Also, what I understood from the article is that the El Rey Network is considering two options: either renew the show or re-introduce it in a different format with the same actors. I guess dropping the show all together then is not an option which I consider to be good news.
I really hope it gets renewed though.