I got cable broadband with premium speed pack but it still drops out a lot. My question is can i bypass the sagecom wifi gateway and connect the Docsis 3.0 to my Netgear Nighthawk R9000 router ?
That shouldn't be an issue.
You have our two modem solution? That's the Netgear CM500V + Sagemcom F@st 3864? You should be able to connect the Night Hawk directly into the LAN port on your CM500.
If that doesn't work rigth away, see if you can force the Netgear modem into bridge mode.