It could take a month or two, maybe longer for a latent bud to push. I've had them set dead looking for some time and then push a strong shoot from very low or even from below ground. If you can see a node above ground I'd bet on it's return. But even that isn't necessary because there could be nodes below ground. If there is anything that might block a shoot from below ground you might clear it away. But the shoot will push through all but hardest hard soil.

Crazy! Thanks for the helpful info, fruitnut. What you said will make it easier for me to be patient now. :) I can't see any node (the vine was snapped off flat at ground level), but I ain't afeard now. ;)

Im not sure grapes will develop growing nodes where there arent already some that are dormant, they will grow roots from just about anywhere I think, but they need to have dormant shoots for vegative growth from my experience. I had a situation 2 years ago where about 20 first year vines were planted in a garden and they were growing well the first summer, but we had a very strange winter and got some temps close to 70 in january, then they dropped back to the more traditional ND temps in the following months and all the vines were killed to the ground. It took a while but some started growing again and developed shoots from below ground, but others never did. I dug some of the ones that werent growing up and they had active root growth, white small new roots, but I left them all summer and they never did develop vegetative shoots. So I think that there is a chance your vine will come back, but its not guaranteed.

Derek:

I'd agree, to grow back the vine will need a node with dormant buds. On own rooted vines there usually are nodes below ground.

They will come back!!