Survive stages on them? You're nearly finished! (4,4)
I believe the answer is:
last legs
'them? you're nearly finished' is the definition.
I can't judge whether this defines the answer.
'survive stages on' is the wordplay.
'survive' becomes 'last' (synonyms).
'stages' becomes 'legs' ('leg' can be a synonym of 'stage').
'on' means one lot of letters go next to another.
'last'+'legs'='LAST LEGS'
Can you help me to learn more?
(Other definitions for last legs that I've seen before include "Final dregs of energy - of lower limbs?" , "Final Limbs denoting ebbing strength" , "Things are bad when you are on these!" .)