I don't see any cracks - could you label them, perhaps get a higher resolution image?
Depending on the coolant in your heatpipe, you may or may not have noticed it leaking. If it is indeed a crack...there's not a whole lot you can do about it.
The scratches look pretty typical of that kind of heatsink. You can sand them out if you want (but it takes great care and precision to do so). There's not much you can do about the dent either.
I suppose you can try and fill the cracks with solder and sand it...but really I've no idea how you could fix it. I'd replace it if it was under warranty.
if they are cracks then the liquid will come out and that heat pipe will be useless, however if they are scratches it will just be a slightly poorer thermal contact between the cpu and hsf and you might lose 1C? maybe 2C?
From the looks of it, they're scratches. The bottom silver part is not a heatpipe, and if you see that part with the same effect on the pipes, then logic serves to show that what you're looking at are, indeed, scratches.
Depending on the kind of pipe, they're filled with a liquid (which, in their state of near vacuum turns some of the liquid into a gas).
I have no idea if it's harmful, but unless you inhale it directly I doubt a leak would cause any problems health-wise. If there is a crack and the liquid looses pressure then it will vaporize and reduce the effectiveness of the heat pipe, probably quite significantly.
each pipe is separate, so loss of one pipe will have an effect, probably significantly less than a 25% reduction probably more like 10-15% reduction in effectiveness.
they are more likely to be scratches than cracks though, they'd have to be approx 1mm deep to breach the pipe. the fluid might be nasty, but it'll be a very very small volume and will have probably dispersed by now, I wouldn't worry, but thats just my opinion.