WHAT WILL HAPPEN IN EGYPT IF THE MUSLIM BROTHERHOOD WINS?

I suspect at the least increased hostilities, and possibly war, with Israel.

Here is an interview from MEMRI TV in which an Egyptian commentator on the Muslim Brotherhood says that the MB do not need public support to start a war. They are obliged to start war on Israel.
http://israelmatzav.blogspot.co.uk/2012/05/muslim-brotherhood-ideologically.html

And late last year the MB held a Kill The Jews rally in which the MB promised, repeat promised, to "one day kill all the Jews".

Egypt’s Muslim Brotherhood, which expects to win at least a plurality in Monday’s legislative elections, held a “kill the Jews” rally in Cairo Friday.

Thousands of supporters attended the pre-election rally at a mosque on the Muslim Sabbath, promising to “one day kill all the Jews” and wage war against Jerusalem’s “Judaization.”

[source : Muslim Brotherhood Holds ‘Kill the Jews’ Rally on Election Eve, INN, http://www.israelnationalnews.com/News/News.aspx/150126, 27/11/2011]