I doubt it will be anything to do with Netflix. it is the app that controls casting not them. Other than them removing the facility from the app entirely.
Have you tried some of the other things in that link I provided under the top section about not seeing the Cast icon?
Another thing to try is a complete power off and back on on the iPad, ie press the power button till you see the Power Off slider, use that to completely power down the iPad. Then restart it. That might reset any funnies with other software on the iPad that is conflicting with the Netflix app.