In general, the way to objectively determine if software works is to give it to those pesky end users, have them use it, and tell you if it works or not, and how well it works. Lacking end users, have testers and QA folks who play the role of end users evaluate it.

In some areas of software development, such as heavy duty algorithmic/mathematical programs such as encryption, video compression, computer graphics, there are pretty rigorous objective ways to measure whether the program works and how well, without human testers or QA people. Usually best to do both even in these cases, just in case there are some subtle issues that the performance metrics don't capture.

On the other hand, predicting the future is noted for being rather hard. Predicting correctly whether a program will need to be changed in two years, in what way, and whether the program can in fact be changed easily all two years in the future is speculation, a matter of opinion, rarely objective at all.