Flag up? Make a speech and disappear (9)
I believe the answer is:
evaporate
'disappear' is the definition.
(I've seen this before)
'flag up? make a speech' is the wordplay.
'flag' becomes 'pave' (as in to pave with flagstones).
'up?' says the letters should be written in reverse (I've seen 'upped' mean this (in down clue, made to go up)).
'make a speech' becomes 'orate' (I've seen this before).
'pave' written backwards gives 'evap'.
'evap'+'orate'='EVAPORATE'
'and' is the link.
(Other definitions for evaporate that I've seen before include "vanish" , "let off steam" , "Disappear into thin air" , "Change from liquid to vapour" , "Turn liquid to gas" .)