Let us focus only on the depreciation that occurs before the project is completed. We simply use Moore's Law. If it takes 18 months to complete a project then the value of the technology components in the project are only half what they were when the project began. This does not mean the project itself is half as valuable because the value of the project is based upon its benefits to the firm. The answer is that nobody knows for sure and it certainly varies from project to project.
Some estimates suggest that half of all technology projects fail.
And every project can recall some users who refused to adapt. The numbers could be much greater or much less than used in the examples above. The only certain thing is that these risks should be quantified and included in any software development project cost calculation.