I forgot to protect my backyard grapevine from upper 20s night time temp and now the leaves and baby fruitlets are brown. What (if anything) can I do to encourage regrowth? Is it possible to still get fruit this year? It has been in the ground for about 3 years and last year was the first year it produced enough to harvest.

What got damaged is gone, but it looks like you may get some what of a crop. It might still bloom some more. Cross your fingers.
We all hate late Frost's.