Richard,
Many JMT, North Lake-South Lake Loop, and other hikers perhaps will need to cancel. But with your skill set and adventuresome spirit, a bypass I propose below might actually enhance your JMT experience.
Matters are even better for you, as you are northbound in late August and your pack will be light, provided you are planning to resupply at the Muir Trail Ranch.
Plan: Exactly one mile after you leave Evolution Lake, you will be back in the trees and will come upon a hairpin turn to the left in the trail. Stop at this turn and a use trail will be evident (often blocked by a small log). Take the use trail (always staying east of the creek) as you head north. The trail starts to fragment as you approach the start of the Evolution Traverse. Just keep going north through the Darwin Bench. From there, your immediate options are to get over the Glacier Divide by either the Key Hole or Alpine Col and then drop into the Humphreys Basin to join the Piute Pass Trail. Turn left and hike to rejoin the JMT.
A longer option is to ascend Darwin Canyon from the Darwin Bench and go over Lamarck Col. Then descend to the Piute Pass Trail Head.
We might not know what the bridge situation is for awhile, or possible local options to cross. But the above plan would really add adventure to the JMT experience. I might consider it, even if the bridge were not damaged! The terrain in this bypass is really sensational.
Jim