Does it use the same scatter rules as a grenade or does it not explode?

I would say yes, just make sure you have a sort of lay out for yourself and the group

I would say 'no'.

If you miss with tossing a greande, you're throwing the object on a very arcing trajectory, so it's going to land nearby.

If you miss with something travelling on a straighter path, it will only hit nearby if you just missed by a fraction AND aimed low. There's a very low probability of this happening. If I was feeling generous, I might give a missed shot a 5% chance of scattering nearby, but it's really not worth the extra mechanical effort.

Picture it. I fire a rocket launcher at a tank. I miss, and instead of hitting the tank, the shot goes to the left. The missile is clearly not going to suddenly fall out of the air next to the tank. It's going to miss the tank, and then keep going for a hundred yards or more.

Siranui said:

Unless you have elevation or do the classic FPS game trick of aiming at their feet?

Way I see it , Basically Krak missiles wouldn't normally (you have to hit to get it to work ), frag missiles (or other aoe missiles) can if the aimer wants to and isn't aiming at a higher target.

Technically no, the same rules do not apply. Normally this is fine, as it is presumed the shot flies by and runs out of fuel without harming anything. However, you might want to account for it in enclosed spaces, tunnels and the like. In those ind of space a missed rocket is likely to plough into a wall behind the target and explode. The only issue is whether this makes the missile launcher too good in those locales.