If you haven't closed the file you could always CNTL+Z to undo your delete history, or you could try to add another smooth node (apply- polygons-smooth- again) to your model and then go the the channel box and access the smooth node and change the divisions back to "0" instead of 4 or what ever it is set at.
i know i can undo...but i mean if it crashes or something else...i tried applying the poly smooth to it again...took 15 mins of it doing the calculation (i had smooth 3 on...had the deleted history...did another smooth 3...smooth 6 altogether...reeeeeeealy bad thing to do!!!) didnt help though :p
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