Who is to blame for missed deadlines?

Question

Project management

The programmer was making a new function and decided to use a third-party library, integration and the first application - everything was fine, but it took a change in the functions that were in this particular library. This could not be done either immediately or after a small parsing of the library (it is a little confusing).
Option 3:
1) Look for another library (without guarantees of success, of course)
2) Write your own analogue (long)
3) Roll out without this functionality (generally possible) and finish it
later there was no time for such an emergency situation.
Who in this case is to blame for the failure to meet deadlines and why? There are no seniors, testers, who would control the programmer or help him. One programmer and one project manager (aka marketer).

Answer 1

and there was no time for such an emergency situation

Then the manager is to blame.
You have two options: a manager, or a manager and a developer.
But the manager is to blame anyway.