Nero was a easily manipulated moron, with a powerful weapon system. Janeway would have baited him into a position where she could have either destroyed him, or better still strip him of his only asset, the Narda.
Maroon him and his crew somewhere.
And if Nero emerged in the delta quad, he never would have captured Spock's ship, and would have never acquired any red matter, so he would only have his ship's original weapons.
No red matter.