Q. In regards to the shayiles sent on mistakes done under the chupa, I was at a chupa where the mother of the kalah, when the cup of wine was given to her to give it to her daughter, by mistake she drank the whole cup herself, what do you do then?

A. Horav Shlomo Miller’s Shlit’a opinion is that is is of no consequence, since the brochos were recited over a kos yain and the chosson already drank from it.
The same would apply if the cup spilled after the end of the brochos and only a few drops were drank by the chosson. The brocho recited on the wine would not be considered in vain.
If the cup of wine spilled completely, before the brochos ended. The Rov advises to refill the cup again and have someone else, from the guest recite a new brocho at the end. He should spill a few drops on his fingers and thus have some of the wine, before the chosson and the kallah drink.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a