We are starting off right after the final episode of season 4. In other words, Lucifer is rising as we speak, Lilith was killed by Sam to break the final seal, Ruby was then also killed by Dean.
Castiel is battling an arch angel with Chuck and their fate is yet to be known. He has gone rouge and his new mission is to help Dean and Sam to send Lucifer back to hell where he belongs while trying to avoid the angels who would drag him back to heaven for punishment for his disobedience.
If someone was dead at the end of season 4 or before, then they are dead here. The only exception is Alistair as he will be needed for a plot in the future.
We will be going from here, keep looking back for more information that will be coming soon