Some operas, a blessing that could disappear? (8)
I believe the answer is:
erasable
'that could disappear?' is the definition.
(something erasable can be made to disappear)
'some operas a blessing' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ERASABLE' is hidden within 'operas a blessing'.
(Other definitions for erasable that I've seen before include "Real base (anag.)" , "that can be effaced" , "with potential to be wiped out" , "Capable of obliteration" , "Temporary" .)