You can't predict software errors, the same way you can't predict car accidents.
As programmers gain experience they learn from their previous mistakes, but make more sophisticated errors.
Number of changes per file
Not a good indicator of anything. The changes could be from additions or bugs, typos or logic errors.
What is a file? Some files have multiple functions and lots of lines of code. others may have a single function, with even more lines of code, or maybe almost no code. Some others may be header files that don't do anything, but are needed for compiling.
(If the above means nothing to you, then you need to get up to learn about it, as I wrote here.)
Imagine deciding the value of a car based on how often it was washed.
Developers who left per file
I have no idea what you are trying to infer from this metric. Sounds like trying to predict the popularity of a fast-food joint based on how many quarters they gave as change.
The rules about bugs is to test from early stages of development, and to keep a 1:1 or 2:1 ratio of programmers to testers. Then you can safely assume the testing-debugging stage will take as long as the time originally estimated to write the code.
The later you start testing and the fewer testers you have, then more bugs will live and start growing in the software and the debugging stage will take longer. Then you can double or triple the testing/debugging time.
Because fixing code that was written recently (today) is easier than fixing code written a while ago (days, weeks or months). Code that's not fresh in a programmer's head needs to be re-read and understood.
Newer code is often based on older code, so if there's a mistake earlier on, it may waterfall all the way down and cause trouble everywhere.
Lastly: Number of bugs is not a good indication of anything, unless you factor in their severity, importance and impact. Both a typo and intermittently crashing the system are important bugs. One will take a few minutes to fix, the other may take a real long time, as intermittent crashes are almost impossible to recreate and find.