Aragon wouldn't object. They might even be willing to ally for the situation and get something from Castile in exchange for their help. At this point, Granada is entirely surrounded by Castile to the point where Castile already holds Ceuta. Maybe Aragon wouldn't like Castile its Mediterranean holdings, but it can do little about it; once again it is best to keep Castile happy.Without the unification of Castile and Aragon would Castile be in a position to conquer Granada or would Aragon object?
Also without the resources and conquest of Granada would Columbus find a receptive audience at Castile court? He had already been refused by Portuguese who secretly had already discovered maritime route to Indian Ocean around Africa. Would he turn to France or England?
The lack of unification would have a huge impact on the new world and the conquest of its two largest native empires Aztec and Inca since any Castilian or other contact would be later.
The resources Columbus asked for were next to none; three ships and crew for a crazy venture. Castile might still be open, as long as the war against Granada isn't prolonged. At most Columbus would have to wait a couple of years, but by then I assume some Portuguese explorers would have already noticed the Brazilian coast as they try to circumnavigate Africa.
England might be open since they were open to sponsoring John Cabot shortly after in OTL. There were enough sailors with enough crazy ideas looking for sponsorship that crashing into the Americas would only be a matter of time. At most your looking into a 5 to 10-year delay. Diseases would still ravage the local population, and the end result might look different but would feel very similar to OTL.