Yes, he will fight against this. I suspect Trump may see him as the replacement for both Sessions and Rosenstein. Sessions has to be near the top of the list of biggest disappointments of Trump’s picks.
Dershowitz is around 80 yrs. I doubt he would be interested in such a demanding role, although who knows? He has previously said he is retired.... but the chance to top off his career as AG might be too tempting to pass up..... but he is ultra-liberal on most issues. Ultra-liberal/left on almost all issues except Israel’s defense and some quasi-libertarian/constitutional issues such as restraining Mueller. Even though he is helpful with advice about these Mueller issues, he could be dangerous in many other ways. I don’t know that Trump would or should really consider him for AG. Much more likely just to get some guidance for the Trump legal team....