Columbus is hardly irreplaceable. Even if he dies and e.g. Cabot's expedition (funded by the Merchants of Bristol, as were several other late 15th century expeditions) doesn't happen, the Portuguese are still busily exploring away. OTL Cabral discovered Brazil in 1500 while en route to India, so America is likely to be found within a decade anyway. It may take longer for others to exploit it and find the Aztecs and Inca, but it will happen in not to long.
The big question for the Old World about a delayed discovery of America, is what happens to Spain? If Spain doesn't manage to stake a claim to the New World riches, then they are probably weaker, and certainly more focused on Europe, including Italy and the Low Countries.
A fun butterfly involves the Charles VIII's Italian War. OTL, the French Army, after seizing Naples in 1495, was devastated by an outbreak of syphilis, possibly brought back from the New World. If that's delayed, the French might do better, and end up retaining control of more of Naples. Or maybe not, but it's an example of how a few years of delay could change things.