Blizzard's complaint with Stratagus was mostly with the original name, "Freecraft". When they took "Craft" out of the name, they were mostly left alone, and the project continued onwards.

>In June 2003, a cease and desist letter was received from Blizzard Entertainment, who thought the name Freecraft could cause confusion with the names StarCraft and Warcraft, and that some of the ideas within the engine were too similar to Warcraft II.[3] The project halted on June 20, 2003

My biggest recommendation to the OpenDiablo and other Diablo clones? Rename it as soon as you can... to OpenDemon or something. It at least gets you away from Blizzard feeling as if they need to defend their trademark, to ensure they can successfully defend their trademark in the future.