Gallery termination is a blessing (7)
I believe the answer is:
godsend
'a blessing' is the definition.
(I've seen this before)
'gallery termination' is the wordplay.
'gallery' becomes 'gods' (I've seen this before).
'termination' becomes 'end' (I've seen this before).
'gods'+'end'='GODSEND'
'is' acts as a link.
(Other definitions for godsend that I've seen before include "Welcome good fortune" , "Very opportune thing" , "The relief" , "Something unexpected but welcome" , "Very helpful thing" .)