Islam does not have a hierarchy. Imams are simply considered more learned in Islam than others and usually are clerics who head prayers in mosques and give Friday sermon. In truth, where many of them do know more about Islam than the layman, some of them just have no clue whatsoever and take it as a job like any other (government pays salaries, etc). Some Imams are even pretty much despised by Muslims. Adherence to Imams is also varied, we have nothing in Islam that makes adhering to a fatwa or Imam compulsory. Usually a person would have a couple of Imams that he admires and "usually" abides by their fatwas, again, with nothing forcing him to do so.

In Shia Islam, it's a bit different because Al Khomeeni is considered a legislator like the prophet himself. So his command is supreme and absolute and you'd expect most Shias to abide by it. Other Shia Imams vary in popularity and usually have some committed followers in varying numbers and their Imams too have a hierarchy usually leading up to Al Khomeeni. In reality, you will find Shias who would not follow these Fatwas, but they are a minority. And again, Al Khomeeni is undoubtedly learned in Islam to make stupid Fatwas. I'm a sunni, not a Shia.

Finally, yes, the fatwas do pose a risk to these people. There's no way to say otherwise. But at the same time, the moderate more learned Muslims always follow up. Where sentiment reigned supreme at the beginning of the event, now religion/logic is catching up to tell these brainless idiots that they've screwed up badly. Many supporters of the latest events have even recounted and realized their mistakes. But alas, a little too late. Islam, through its teachings, forbids the kinds of actions that happened in Libya (check my previous response for sources). I'll try my best to spread the letter that's been passed here.