Andrew Murray, for starters, was a noble, being born from the prominent Murray family, and heir of a leading baron supporting the Comyn family (1) And compared to Wallace, who was lower gentry and just a common landowner (and depending on which account of history you read, he is either the son of the Wallace clan chieftain, or a removed cousin of said chieftain). Being medieval history there is a common chance that Andrew Murray would have taken the lead simply because he was a noble.
Also, it is speculated that Andrew Murray was key to the Battle of Stirling Bridge because he had had previous battle experience battling the English fighting for Balliol at the Battle of Dunbar, and his tactical expertise was key at Stirling. His death apparently was one of the reasons considered for Wallace's loss at Falkirk (2). So there is reason to soncsider that if Murray survived that he may have been the leading man in the fight against the English.
But in terms of being able to beat the English, it really depends. Edward I Longshanks was rather a powerful figure in medieval England. OTL History confirms this, and considering his success in both Wales and Scotland - even in England in his early years - the scots may have a hard fight on their hands. Murray though certainly was an equal to Edward I in many ways, so he may have put up a hard and decent fight in order to seek independence. Indeed there is probably a decent possibility that he may have succeeded had he lived.
Here are a couple of websites that may offer an opinion:
Look here:
http://en.wikipedia.org/wiki/Andrew_Moray#Death
And Here:
http://www.ltscotland.org.uk/higher...nce/wallaceandresistance/historicaldebate.asp
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(1) Scotland: The Story of a Nation, Magnus Magnusson, pp134
(2) Scotland: The Story of a Nation, Magnus Magnusson, pp139