The link to fornebu is broken and can anyone tell me what happens when your credits run out

Which link are you talking about? I tried the one on the portal and it directs me to the right site. The URL is working too.

When your credits run out, most of the game’s features are locked until new credits are bought. See this wiki page for more information.

does that include the basic features such as buying aircraft or creating routes

Yes, basically if you run out of credits, you can’t play the game until you recharge your account.