What happens when a phase gets disconnected in a 3 phase four wire and 3 phase three wire system?

Can u imagine a merrygoround with so many kids on it that three kids can hardly turn it? now imagine that same merrygoround with only two kids trying to turn it. Same thing with one line missing. it will sit there and burn until a breaker goes or the other kids burn out.

If you have a motor running it will run until it is stopped but it wont start again.

motors;

called single phasing,, the other 2 phases ampers increase and trip the motor overloads.. or blow fuses