Ah, an interesting choice.
The 1877-78 war secured Russia's presence in the Balkans, and set the stage for over a century of regional geopolitics. Russia sought to impose itself as a defender of local Christians, a very dubious obligation it had held down since the 1820s. Putting aside the root of Russia's caution here - it would have to wager the loss of a degree of propaganda face I'm not convinced any Romanov would be willing to stomach - the butterflies are, obviously, going to be enormous. I could see a feel-good Austrian intervention to fill the void, though the campaign would likely be be more limited (nobody in the West, so to speak, had any interested in a crippled 'sick man of Europe' - an occupation of Bosnia-Herzegovina, perhaps?). Crucially, it could also merit Anglo-French sponsorship, something the Russians really had little intention of doing. The Ottomans may or may not fail to crush the revolts against them, and I wouldn't bank on anything given their dreadful performance IOTL.
The major result of this would be Austrian, rather than Russian predominance in south-eastern Europe, with Vienna presiding over a host of ethnic quasi-protectorates. A three-way cold war between a resentful Russia, bent on conquest (and with the potential sympathy of Orthodox Bulgarians and Serbs), Western darling Austria and a crumbling Turkish empire would make for a fascinating read.