Michael Rosenbaum is definitely leaving. There's an open letter to the fans thanking them for supporting him for the past 7 years.

In his place, 'Doomsday' and a female antagonist will be taking over as the shows main villains. I have no idea how hat will work, considering Doomsday doesn't even speak, but this really doesn't bode well for the final season

DOOMSDAY, one of my most liked supes baddies as he is the only one in a million years that can get a decent fight out of our blue boy in tights, although you are right, he dont speak and it will take some doing to have him appear every episode with CGI and all that I hope they do him justice but this does sounds a tad annoying.

i dont want Michael Rosenbaum to leave i love him as lex

Just saw APOCALYPSE, liked it, will comment more, this is just for a reminder to self, ps there may be spoilers so if you have not seen it then please try NOT to read.

Kristin Kreuk will also only be back for a maximum of a 3rd of the season which for me is fantastic
This means they should have erica durance as their leading lady for the last series since she is lois after all and i hope her contract gets upped to a full series

is chloe going to be in the next seires

Possibly, a number of the cast will only be appearin breifly in season 8. Inclduing Michael Rosenbaum, Kirsten Kreuck, possibly Allsion Mac (not sure how much of it she will be in). I am not sure if john glover will be in season 8, you would have to take that up with one of the other smallville veterans.