I know Shu He deceived Zi'Ang that he'll drink the poison and the dr has its antitode and then when he'll be dead…
initially the plan should be like that, the ziang knew it, once he was out, he will find him outside but then in the last min, he and dr planned it without antidote, so real death to revenge ziang what he did to him, so ziang noticed different, and rushed to him after he drank it and smiled
the best realistic ending even not everyone happy about it,
either both of them pretended to be dead and runaway (but ziang will died early anyway), or both of them died together as shuhe cant forgive himself to be alive as he was guilty that his lover was the causes of his broken country and people losing their homes and live
since both of them died in the novel, but director said they changed it to HE, so i guess, they both of them pretended to be dead and hiding somewhere where no one else to know who they are and they are happy ever after like what shu heng always wanted