All perfect praise be to Allah. Blessings and peace be upon Prophet Mohammad.
If it was proven beyond any doubt that a substance had been soaked in wine, then it is impermissible to use it in any kind of food because Allah The Almighty has absolutely proclaimed having wine as illegal and has also rendered using it in any type of food illegal. He Says in the Holy Quran: “O you who believe, verily wine, and games of chance, and idols, and divinatory arrows are an abomination of Satan's work; so avoid it, so that you might prosper.” {Al-Mai`da/90}. Prophet Mohammad (PBUH) said: “ Allah has cursed wine, the one who drinks it, the one who serves it, the one who buys it, the one who presses it, the one pressed for, the one who carries it , and the one carried for.” [Abu Dawood/ related from the narration of Ibn Omar (May Allah be pleased with them}.
However, if it was proven otherwise, then it is permissible to use it (vanilla) since, in principle, things are permissible so long as there is no Sharia approved evidence that they are forbidden. And Allah Knows Best.