When all else fails! (2,3,4,6)
I believe the answer is:
in the last resort
'when all else fails' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for in the last resort that I've seen before include "when all else was unavailable" , "how anagram was finally resolved?" , "finishing off a tour?" , "Where one spent the previous holiday" , "Where tour party ends up" .)