If something is suffering the death of a thousand cuts, or death by a thousand cuts, lots of small bad things are happening, none of which are fatal in themselves, but which add up to a slow and painful demise.
If people try to make fun or laugh when things are very frightening, dangerous, life-threatening or hopeless, it is gallows humour (or "gallows humor").
If you give someone enough rope, you give them the chance to get themselves into trouble or expose themselves.
(The full form is 'give someone enough rope and they'll hang themselves)
'Knock 'em dead' is used as a way of wishing someone luck before they give a performance or have to appear before people, as in an interview, etc.
('em = them)
Someone who by virtue of holding a position of trust with an organization for a long period of time has come to know many of the secrets that others in more powerful positions would rather be kept secret knows where the bodies are buried. An implication is that the person knowing these secrets will use that knowledge to secure something of value for him- or herself.