Rivnuts from Homestead, PA on 1/9/2020 3:25:43 PM:
Rt 340 is fast and fairly heavy traffic (at least west of HF which I rode in route to Harpers Ferry (HF)) with some sections where the shoulder narrows. Depending on your tolerance for car traffic, it could be a little daunting.
Shepherdstown would be a fine alternative overnight albeit without the same historical significance but very quaint in and of itself.
Given the historical significance of HF and the traffic from both the C&O Canal Towpath and Appalachian Trails, I would expect that local officials will stress the importance and timeliness of repairs to the pedestrian portion of the bridge by CSX Railroad. I'd keep a close watch for plans and progress which may enable you to maintain your plan to visit HF without traversing Rt 340.