Sayid will die in the finale as a result of having to manually detonate the bomb. He has nothing to live for after Nadia died and he wants to change the future just as Jack does.
Sayid thinks that detonating the bomb will cause the magnetic anomaly to cease and hence thinks Oceanic 815 will land safely in LA. This is incorrect, in detonating the bomb Sayid will cause the incident and indeed make Oceanic 815 crash in 2004.
The death will be tragically played out such as Charlie's. It will be made out that Sayid is sacrificing himself for everyone, knowing that he will land in LA in 2004, but then Jack will realise that he and Sayid caused the incident and Sayid died for nothing.