Is it possible to execute two or several tasks in parallel with a microcontroller e.g. a PIC?
Why do you think it is not possible? Functions can be called and not using functions leads to undecipherable spaghetti code. There are both professional quality designs but also beginner hobbyist code so you can find both. Some extremely tiny microcontrollers can have a limited hardware stack so subroutines are not used much, even if it is possible.