Update: another, smaller closure from July 21-July 30th.
Both Biking Bis and the Seattle Bike Blog are reporting the repair work will close a portion of the Snoqualmie Valley Trail through the end of October. The closure is on a stretch between Duvall and Carnation, and because the only parallel is Rte 203, a very busy and narrow-shouldered road, that's not a particularly safe option. However it is possible to detour, as one of the Seattle Bike Blog commenters pointed out, but hopefully this will be the last closure for a while. The suggested detour route, although there are others: