My suggestion:...wer auch immer da leben oder sterben mag
I've read this book. The sentence is much more intelligible if you know the situation of the character speaking. It is soap opera pur, as one would expect from Trollope. (Thankfully, it is the merely back-story and not really what the novel is about.)
"When I gave him my hand then as he parted from me, I gave it him as his own. It has been his to do what he liked with it ever since, let who might live or who might die."
At that moment (when she held out her hand for "him" [to clasp/bow over..in farewell]), she put her life/heart/destiny into "his" hands and it remains in his hands now, regardless of who might still be living then or in the future AND regardless of who might die at some point in the future.
At the time of which the speaker is speaking, both the speaker and "he" know that they love each other, but they have not confessed that love to one another aloud. The "who"s in the sentence refer to the speaker's husband and her husband's brother. Shortly before the moment of which the speaker is speaking, the two unavowed lovers have heard that one of these two brothers is dead (i.e. either her husband or his brother is still alive). At the time the speaker is talking, she knows that, contrary to the report they had at the time, both brothers were still living at the moment of which she is speaking, but she has recently heard that her husband may have died in the intervening period.
