While he was more liberal than his successors, he was still a conservative. Don't expect the Duma to get any kind of real power; it'd be like an even more autocratic version of the German Empire. And the reactionaries who would succeed him in real life are still alive, so I wonder how much leaving him alive would truly solve. Chances are that any moves made towards any kind of liberalization, however small, would be reversed or limited by Alexander III.
He was rather fond of Germany, however, so we may see a different alliance system develop, or at the very least get a Russia which is less eager to stand with France against their monarchist pals.