Whilst I don't know any other assassination attempts apart from the one already given (a testament perhaps to the power of the Kim cult of personality), arguably the greatest crime a member of the party (an accolade only given to the elite) or someone on the top of the songbun class system can do is defection, which is becoming more and more common as North Korea slowly laxes it's border policy's and technology is becoming more available.. Individuals who defect are denounced as traitors, and any members of the person's family up until the third generation are sent to "re-education camps" far north in the mountains near the Chinese border, most likely never to be seen again.

(Source: The Impossible State: North Korea Past and Future by Victor Cha)