I asked the Dev's a while back if they would be in game and they said doubtful at launch. So the question is

yes atleast, passive flyer.

No player controlled flyers.

I was asking about useable like the storm talon and equivalents . I think it was mentioned that there maybe a passive one in like a thunderhawk or equivalent

Would love to see some, why not? They're working in Planetside aswell

On the plus side, flyers would be exciting to use on such large battlefields.
However, flyers could be too large of an advantage and could put off large melee battles...

Not at first no, but maybe real time transitions between ship and battlefields.

Just asking, in case friendly fire would be enabled, do you think randoms would still fire into a big Close combat with rocket pods?

Never stopped me from doing it in Planetside 2

Balancing is hard enough in such a game, and Planetside 2 had a lot of problems of balancing the aircraft, so one day they would rule the skies, while another they would get blown up immediately. I think it's better for the game as a whole to just leave flyers out of it, as they are not nearly as vital (in my opinion) in 40k as they are in f.ex. Planetside. It will be easier to balance and the server load will be considerably lessened, which means better performance overall for us players.