A chainguard might help some. I'm sure it's really beneficial to protect the chain from rain if the bike stays outdoors. But unless you're talking about a full chain case my chain is still going to get doused with a salt, water, and sand mixture on many of my winter commutes. I can clean my chain one night and the morning after my next commute it'll be rusty. It all depends on the weather of course. If stays cold, it's not as much of a problem but when starts getting into the 20's the roads will be slushy and wet.

I've used some KMC "Rust Buster" chains that help keep the rust at bay, but they still need frequent cleaning and lubrication to manage the grit. The pins still rust. Even with the rust busters I won't get much more than a season out of them. They won't look as bad but they'll be just as worn.

I think a belt is much better suited to the conditions I ride in during the winter.