Even if the zig zags are iced up, go to the bottom of the zig zags on one path, and back down by the other.....? And, if there is snow,think carefully about the obvious alternative of the Llanberis path - the slope is concave above the halfway station and is very dangerous in case of a slip/fall on snow and ice.
A posibility is The Snowdon Ranger path. Oh, but beware that the cafe is closed for rebuilding - so if you were thinking of grabbing a cuppa whilst up there you'll have to take your own!
