speaking as an astronomer.... yes, its possible... given the correct precursors and triggers.... true the orbits of neptune and pluto are on different planes, but there will be a time when both will occupy the same point... when is a matter for conjecture... also, given that orbits decay, even solar ones, and the chance grows... if you accept that pluto is not a planet, but an asteroid, it also becomes easie to believe, as is the idea that neptune could capture pluto, with pluto then becoming a moon of neptune... collisions in space happen all the time... earth has just been lucky so far... not long now and we'll get hit....
All that beautiful physics and it's laws needs to be considered. I remember we had a long off-topic discussion about this same topic, and I recall my teacher saying that it's very unlikely to happen because the calculations at which here two planets will cross each others' orbitals needs to be exact...
So basically, it's a possibility; but I don't think we'll see it happening in out lifetimes most probably, and hopefully. 😛
Well... if pluto hit neptune, neptune would collide with uranus, making this big ball of DEATH! That ball, in turn, would collide with jupiter, in turn increasing it's mass by 30% (give or take) and AGAIN in turn ignighting it, causing a second sun, and KILLING US ALL!!! ..... but that won't ever happen... ^-^;;