What happens if you put a non-native firmware?

Question

Mobile devices

There is a "lenovo a319" phone, the firmware often flies, I had an idea, but what if we put the firmware on this phone from asus, prestigio or samsung? From here the question arises, will it work?
Question 2: I heard a lot about the fact that if you do not flash the phone correctly or use a "clumsy" firmware, then the phone will turn into a "brick". How sad is this state of the phone ("brick"), and is it possible to get it out of this state?
PS Thank you very much!