Unlikely if you ask me. He lost the nomination to Jospin despite being at the head of the party and there were very good reasons for that. He was a bit too much to the left and - probably more important - he was a party-man nobody knew outside the party.
Now assume he is chosen by the Socialist Party. To have a chance to win he must compete against Balladur. Chirac is too much of a "political beast" to be really threatened by Emmanuely. Say Baladur avoids afew mistakes and win the first round by a narrow margin. Chirac sabotages his campain and Emmanueli wins.
His policies will be more to the left than OTL Jospin's but probably not much. What one can expect, however, is an opposition to the strengthening of the EU (he won't go out, however) and less societal reforms (the PACS won't probably pass)
Another difference will be his relationship with the parties of the "plural left". The greens will be less influent (which might save them on the long run) and the communists keep more posts in the government (which definitly won't stop their fall).
Of course he won't dissolve the parlement in 1997 so we'll get a right wing government in 2000