Long-dead people -- some reincarnated (4)
I believe the answer is:
inca
'long-dead people' is the definition.
'some reincarnated' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'INCA' can be found hidden inside 'reincarnated'.
(Other definitions for inca that I've seen before include "Ancient South American" , "Pyramid builders" , "who lived in S America" , "Native Peruvian" , "Ancient Andean Indian" .)