I'm a bit curious about this thing. I know in NPN BJT transistor, current flows from collector to emitter since the emitter usually connected to the ground (please correct me if I'm wrong). What I want to ask is, in the worst case (assuming severe transistor failure,) is it possible for current to flow from emitter to collector(assuming that the collector have lower potential or connected to ground) and the emitter have higher potential compared to the collector?
in the worst case (assuming severe transistor failure), is it possible for current to flow from emitter to collector
You don't need to assume transistor failure for this to happen. If you swap emitter and collector terminals, you will get an operational device but, it's β will not be as high as a normal connection. However, it will saturate to a lower emitter-collector voltage when driven hard and, occasionally, I've seen engineers do this (despite it looking a little odd).