With a POD after 1825, where Nicholas I has been crowned Tsar, what is the best case scenario for the Romanov dynasty. It does not need to be an absolute monarchy at all, it just cannot be shot to death by Communists.
Nicholas Alexandrovich (Alexander II's oldest son) survives and AII lives to 1890's and dies natural causes. AII gives 1880's constitution and Nicholas II (Alexander II's son) makes that stronger and Russia transfer slowly towards British style monarchy. Probably tsars has still much power but Russia is more democratic, more stable and more prosperous. Living standards of common people are higher.
Essentially get more competent heirs, either by abdication or disinheritance perhaps or stronger traditions of training. Alexander III modernised and centralises the state even more.