As far as I can tell, I can't do this. I can't "undock" items from within MM. However, and I'd place a bet on this with you, that you have:
EITHER
1/- Inadvertedly Double Clicked the separation Border between your Search results Pane AND the Search Pane.
OR . .
2/- Inadvertedly pulled one of the panes "across" the Search pane.
If it is either of these the easy remedy is EITHER to hover the meece over the edge/border of the Results pane, wait for the DOUBLE-HEADED arrow, Left Click HOLD and drag to the right - this should bring it back OR double click on the Search Results border. That should do it too.
However, if you have the earlier version of MM - 2.0 - there is a PUSH pin that I gather you can use to summon up the "other" panes . . or is that PAINS!