its kinda hard to explain this without introducing the concept of phasors.

i phasor is a quantity that has magnitude and phase angle and phase and theese can be represented as the distance and direction from the origin on a phasor diagram

in a 3 phase supply the three lives are equal distances from the origin and the angles between all of thier directions are equal.

in a 3 phase system with balanced linear loads there will be no neutral current.

and in such a balanced system removing the neutral connection will have no effect since it wasn't doing anything anyway.

HOWEVER real life is NOT so nice

loads will be unbalanced and in some cases (particularlly anything involving AC-DC conversion) will also be nonliniar.  the neutral wire serves to keep the neutral point of the load at a fixed point relative to the phase wires despite the non-ideal load configuration.

with linear loads the most voltage an appliance will see in a lost neutral situation is the systems phase-phase voltage (this will happen if one phase has a far heavier load than the other two it will get almost no voltage and the other two will get the full 415V)

however nonliniar loads and switching of loads where inductive loads are present on other parts of the system can cause HUGE transiant voltages in this situation (spikes in the range of kilovolts are not unheared of)

in a large well balanced system the most noticeable affect of a lost neutral will probally be lightbulbs blowing sooner because of spikes. in smaller less well balanced systems the more sustained overvoltage from the imbalance is likely to be the destructive factor.

And this is going to happen loads and loads more.

Why?

Part L & downlighters that's why.

All those energy efficient fittings & the LV trannys with their associated harmonics can give an RMS Neutral Current value 1.7 times the live load. Now you do that across 3 or 5 phases of a distribution system and watch the under-sized Neutral curl up like a spider in the candle.

I really reckon there'll be stacks of remedials in the future. Followed by draconian limits after a few good brown-outs in large cities. Then there'll be Part Zed or something.