For other races or even dalish, maybe. For Tabris? Unless she doesn't care a damn about her people's dignity, NONE.
Even if she only cares about herself, it's stupid to let him live. No matter what, she is still an elf, that can't change. Her people's humiliation eventually would be hers, too, whether she likes it or not. Even if she makes a deal with Anora and manages to grab some power, that would be precarious, since all other people see her as someone from a race which people could sell as slaves virtually with impunity. Thus, for a Tabris, more than any other origin, it's imperative to get rid of WHOLE Mac Tir family for good.
Tabris and Mac Tirs are implacable enemies, whether for morality or real politik.