[Yosemitest]

"ISON is/was moving at 151,088 mph"

You really need to keep up.
As it got closer to the Sun, the Sun's gravitation pull causer it to speed up.

[FreedomStar3028]

I am caught up..... that is how fast the comet would be moving right now, if it’s there. The hubble will be trying to locate it if it wasn’t completely vaporized in the next few weeks....and no it and none of its debris is going to come anywhere near Earth.

[Campion]

As it got closer to the Sun, the Sun's gravitation pull causer it to speed up

And as it gets further from the sun, the sun's gravitational pull will do what ... ??

(The correct answer is: "slow it back down". When it gets back out to the earth's orbit, it will have the same velocity it did when it originally crossed earth's orbit.)

[Darksheare]

And now as it moves away it will slow down by the same rate.
This happens all the time.