With all the rain lately, the water temps have only been in the 60's. Trout can survive in that. How long it took to get way upstream and how long it will take to get back to the White, I would have no idea. But with the heat we're seeing around here now, the river will warm up and if any trout in the Buffalo don't head back soon, they will die.
Of course there may be a cold water spring flowing into the Buffalo way up river where trout can survive year round.