[Justa]

Of course you must realize that if ISON is travelling 300,000 mph that there is an enormous amount of inertia invested in its trajectory. Any splitting or bumping going on amongst the fragments will be negligible to the tragectory. If they were moving 3 mph, yes. But at 300,000 mph -no.

[Yosemitest]

I don't think so.
When the item is in motion and breaks up due to heat stress, or venting gas, or due to electric/magnetic field "attractions/explosions", all bets are off.