Also as a senior developer you carry some of the responsibility for the junior's ability to make that mistake. You probably set up and maintained the development environment where such an error could slip through into production.

So in case of a critical error/melt-down you should first of all blame yourself and think about why you set up a process and an environment that let this happen in the first place.

Think about what went wrong and how you can prevent it from happening again. When I started at my current place of work, they had a horrible manual deployment process that was the cause of 99% of all problems they experienced. Rarely critical problems, but still annoying and unprofessional. So we implemented automated build, test and deployment process that got rid of almost all of these problems.

Now, whenever something bad happens, we realize it is a problem with the process (not the individual) and correct/improve it as needed.