After googling the hell out of this topic, I could not find a particularly good answer for how to collapse a multiclip.
In Cs6, its not an option. (Though should be in next version.)
To collapse a multiclip, the fastest workaround I have is:
Select the multiclip: it will be named MC[layer #] (i.e. MC).
Shift T to match frame to the multiclip.
Drag the appropriate layer (i.e. [layer 7]) into the source monitor.
close the multiclip sequence and go back to the MC clip.
Shift-option drag from your source monitor onto the clip, replacing the MC with its source clip.