How significant is the static buildup on the blades of the main rotor? And some questions related to this
1) Technically, yes, it's possible to be electrocuted by a static discharge. The chance of it happening is so vanishingly small, though, that it's not generally a concern. A helicopter simply doesn't have the capacity to store enough electrical energy to be a direct danger. The real threat from static electricity is that it can potentially ignite a fuel spill, or something of that nature.

2) Depends on how you define "grounded". The linkages are coated with grease, which typically has a pretty high resistance. This means that low voltage (where "low" in this case can be up to 500 volts) across the junction probably isn't going to generate a meaningful current. However, static charges routinely exceed 10,000 volts, which isn't going to be affected by a thin layer of grease. So, you can generally consider the whole plane to be at the same potential.

3) Same thing that happens if you're on the ground and touch it. When you touch metal, you'll get a spark, yank your hand back, probably shake it a few times if the spark was particularly bad, and resolve not to do that again.