Even Sherpa finally is lost, with trail disappearing (10)
I believe the answer is:
evanescent
'disappearing' is the definition.
(thesaurus)
'even sherpa finally is lost with trail' is the wordplay.
'finally' suggests the final letters.
'is lost' indicates an anagram.
'with' says to put letters next to each other.
'trail' becomes 'scent' (I've seen this before**).
The last letter of 'sherpa' is 'a'.
'even'+'a'='evena'
'evena' is an anagram of 'evane'.
'evane'+'scent'='EVANESCENT'
(Other definitions for evanescent that I've seen before include "not permanent" , "slipping away" , "evaporating slowly" , "Disappearing" , "Passing" .)