If you got the Dom Kavash Device, and Then got the "Get a job" message, with a text saying there's a new hypergate getting built in Altair space, that means you finished the extended campaign. You can still go and search the half done secret Coalition's hypergate
If there'd be a huge gate arround Nephele, you would see it easely. You can see objects at 30 Kms far, depending on your res and options, can be more. But it's a bit harder in Inner Core