Given that one has a shehakol food as well as water and coffee beans, if one makes a shehakol on the other food intending to include the prepared coffee, and only then realizes that the coffee has not yet been
prepared brewed, is the coffee covered?
This question gets involved in several points of dispute.
Question number one is what blessing do you make on coffee, and why?
If you hold like those opinions that the blessing on coffee is Ha'adama (brought in Ba'er Heitev 202:19), then the answer will depend on if a b'dieved blessing does not take effect on another food when it was not a beracha levatala (meaning, you made the shehakol on your shehakol food, and you want your shehakol to b'dieved work for the non-shehakol food). The Shulchan Aruch 206:2 holds that it works, while the Mishna Berura 206:10 cites opinions who disagree. So if coffee were to get a Ha'adama, and you held like the opinions cited in the Mishna Berura, your shehakol would not work. If you held like the Shulchan Aruch, it would work, as far as the issue of making the correct blessing is concerned.
If you hold that coffee is a shehakol, it depends on why it is shehakol. If it is shehakol because the water is the primary element and the coffee is just a flavoring (implication of the Shvus Yaakov 2:5 in comparing it to beer, in which the grain does not go into the water, but just flavors it (Tos. 37a s.v. Hai Duvsha)), then the water is the same water and there is nothing to discuss - your brewed coffee is the same water, with a secondary ingredient added in. If it is because the coffee is not edible and is therefore not a real "pri" (this possibility is mentioned in Panim Meiros 2:190) then the coffee is shehakol, and now that it has been brewed, it remains shehakol, but now it is shehakol as the resulting product of the coffee bean, not as the original bean. In that case, you have a "new" shehakol here that was not present before. Even so, I would think the Mishna Berura (206:8) is applicable, namely that if you are explicitly intending to cover a food that is not present, it is still covered by the blessing.
In summary, if the blessing on coffee is ha'adama, then it may not work. If the blessing on coffee is shehakol, then it almost certainly works.