How indeed. 

Sesshoumaru isn’t really the type to let emotions get the better of him, as I’ve explicitly pointed out before. But I think in this particular situation would be the exception to the rule. Being the kind of person that doesn’t often let emotion mess with him, he would have absolutely no coping mechanisms. He’d do his damnedest to prevent it from changing his life, from changing him — to no avail.

Obviously, these attempts would be futile and would end in a serious emotional break that we’ve never seen from him and will likely never see again.