i didn't say anything about a cliffhanger, but i think either venom's symbiote or his spawn, carnage, will stay alive. there is going to be an after-credits where carnage joins someone or venom comes back, that's just how it is, there's going to be another one. the even said that they wanted to make alot.
who knows, just wait another year. it'll go fast if you don't talk about it and forget it.
edit: also, why would they make this on and bring in venom if they were just going to end it here. kinda like how JKR didn't have dumbledore's painting awake at the end of the 6th book. just more questions to answer.