No, you don't need to save it. From the doc,
montage(I) displays all the frames of amultiframe image array I in a single image object. I can be a sequence of binary, grayscale, or truecolorimages. A binary or grayscale image sequence must be an M-by-N-by-1-by-K array. A truecolor image sequence must be an M-by-N-by-3-by-K array.