If its under 50 lines of code for some simple processing, I don't think another developer who comes in would have much trouble. Of course if that 50 lines of code is now 250 because it tries to get around a framework, then instead of finding a PHP developer to help out on the code, you now need a $framework developer.

Basically, don't use a framework unless you really do need all the features it gives you. Don't just pick a framework and try to cram your code into it for the sole purpose of using a framework.