I always let my salvias die from the cold, mulch heavily with fallen leaves, and leave the stems standing until spring. It is windy here, so I cover the three-foot layer of leaves with a piece of chicken wire to hold the leaves in place, and the stems help keep the leaves from compacting too much; I think more air space means better conditions for the salvias. Of course it is much colder here in PA than in much of western Oregon. Still, I would leave at least part of the stem standing all winter even in Oregon.

Mine die all the way back in winter in CA/z9. When all the leaves have turned yellow/brown, I cut them to the ground.

Salvia patens likes it dry when it is in either summer or winter dormancy.

I am awaiting a plant or seed of the selection made by Cabrillo College, which was a 4 foot by 4 foot bush so heavy with flowers that there was a nearly continuous blue carpet underneath the bush.

The top growth of mine just seems to disappear - I am usually still collecting seed till nearly Christmas, then I shove the plants somewhere and forget about them till spring, and by then there's no top growth left! Rots and blows away, I suppose. I don't have to overwinter these under cover but if I am taking some in (to get an earlier start or if very cold weather is forecast) I cut them down beforehand.