I know Steven Erikson has a realist penchant for senseless deaths (Trull, Whiskey Jack, etc) but I think having Tool kill himself to save less than a hundred of his enemies within the Barghast takes the cake, especially when he knows full well what will happen to Hetan and their kids when Maral Eb takes over as War Leader.
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No. They will kill you. And our children. And for me, something far worse. In a low whisper she then asked, 'Shall we flee, then? In the night, unseen by anyone?'
He lowered his hands and, eyes on the storm, offered up a bleak smile that lanced her heart. 'I am to be the coward I so want to be? And I do, beloved, I so want to be a coward. For you, for our children. Gods below, for myself.
His whole motivation leading up to the scouting expedition was to avoid the destruction of the Barghast clans. He was willing to step down as War Leader if that was what was required (but Hetan clearly states above that this is NOT an option if he wants his family to survive.
So his only choice is to continue as War Leader and hope he can convince the clans to avoid this war by scaring his rivals within the loyal clans into changing their minds.
Now when he realises that Maral Eb is about to ambush the party, why doesn't he make a fight of it?
Was his claim to Bakal or Riggis that he could take on a thousand Barghast warriors just a few hours before an empty boast? No... we know that as the former First Sword he was freaking unstoppable... even now as a mortal Imass he still among the best swordsmen ever. Period.
So what are the options open to Tool?
1) Kill himself and thus saving Bakal and the others, but ensuring that Hetan, their daughters will be hobbled, gang-raped and murdered?
2) Lead Bakal and the others against overwhelming odds, but at least offers a small (however insignificant) chance that some of them survive to escape the ambush? If he dies, well the same fate awaits his family, but if he manages to escape to warn Hetan or rally the loyal Barghast - there's some hope of averting the atrocities that await them?
Now as an author, I can understand why you'd want Tool to die so as to set up some other part of the plot - but for Tool to give up knowing he's going to condemn his loved ones without a fight is just not believable. Tool couldn't have possibly known the size (or the outcome) of Maral Eb's ambush. And he's survived impossible odds before. (40-1? pfffttt... cake walk).
At least if he was to die, let him go down fighting. Let him take as many of the enemy with him to the grave. Let him have a proper honour guard of harvested souls before finding his rest. Let Onos Toolan, First Sword of the First Empire, rage against the dying of the light before begging for Hetan's forgiveness as he dies.
At least then he will deserve it.