True hisnagdus to chassidim is obsolete, B”H. There were once true talmidei chachomim who understood nuances of chassidic thought, and took issue with it. Incidentally, I believe that the Gr”A never actually signed the cherem, but that he did not oppose it. The signatores were his talmidim. That might be verified by others here whose knowledge of history is better than mine. Regardless, the belief at that time was that the chassidic movement was a departure from Torah based Yiddishkeit. There were many events since then that have convinced the Litvishe Torah world that this is untrue.
As Yiddishkeit grew in America after WWII, it became clear that chassidus was one of the elements that facilitated transmission of Torah and Yiddishkeit to the next generation. The yeshivishe world eventually recognized that, and the split was recognized to be artificial, and frankly an obstacle to growth. While others might be equipped to identify specific personalities who helped accomplish this, I think it is safe to say that the past several decades have led to the demise of true hisnagdus. For that, we should all be grateful.