This is more of a security question: Are there any circumstances (i.e. running PHP as a CGI binary versus Apache module, examples of poor default configurations, etc.) where Apache would render the unprocessed source code for a PHP script if PHP were to crash independently of Apache?
No: Apache delegates script processing entirely to PHP using some method or another (DSO, CGI, suPHP, whatever). Whatever it outputs, will be treated as the response to render to the user.
If it is going to crash, then most of the time, the process will crash without outputting headers. If it does not output headers (which Apache will know because it won't find a single blank line in the response), it'll render a
If, say, it managed to output:
Then the user will see "Segmentation Fault" on their screen, nothing more, nothing less.
Your question also says:
Yes, if Apache is not configured to process PHP pages, then it will output just dump the file to the user. Other than that, there is no kind of poor configuration that would get you in a half-state where it works most of the time but not all of the time.