Requiem and what it follows that might do for us? (4,10)
I believe the answer is:
mass extinction
'requiem and what it follows that might do for us?' is the definition.
The definition suggests a singular noun which matches the answer.
'requiem and what it' is the wordplay.
I cannot really see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
'it' could be 'sex' ('it' is a common euphemism for sex) and 'sex' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mass extinction that I've seen before include "When many species die out" , "Widespread death of species" , "Sudden loss of diversity" .)