The likelihood of it happening is extremely small at 2^-128. While many have been using BIP32 for years, including Lombrozo, they have never had to handle this case. Some app developers feel that dealing with this level of complexity is not worth the effort. However, if handling the case is easy to implement and isolate in program flow, Lombrozo would be in favor of implementing such a solution. The idea is to handle the problem in the library so app developers don't have to worry about missing addresses or ignore the issue. This could be achieved by having the library retry instead of returning an error.