I am also curious about the question of ‘would be dealt damage’. Do you decide if damage is going to be reduced to zero for the current target to decide if the trigger is going to occur?
There is also the question of multiple redirection and how to deal with these triggers.
One possibility is to think of it in the sense that when an event occurs, triggered effects get generated by all applicable cards and then get applied in the order their cards were played.
Smoke Bombs (SB)
Lead from the Front (LftF).
The card order is SB, LftF. Damage gets dealt to the lowest HP hero. Both cards create triggered effects. SB effect redirects to the highest HP hero. Now the question is what to do about LftF’s effect, does it still give the option to redirect to Legacy? Does the effect somehow disappear, and if so, how does the player know when and how to do it?
The card order is LftF, SB. Damage gets done to the lowest HP hero. Both triggers get generated. In this case, if the SB effect doesn’t get eliminated somehow, LftF can’t do anything because SB is still going to redirect to the highest HP hero.
The card order is back to SB, LftF. Legacy is the lowest HP hero and damage gets dealt to somebody else. LftF redirects to Legacy, does SB still go off?
Another way of looking at it is that triggers don’t actually create effects simultaneously, but in reality what the game is doing is checking each card in play in played order to see if it generates an effect. Once an effect redirects that damage, the original trigger of the effect is no longer valid (the hero in question is no longer ‘would be dealt damage’) so you stop that function and now look at the new situation and any triggers that might cause.
The card order is LftF, SB. The lowest HP hero has been dealt damage. You search the cards and find LftF and choose to redirect to Legacy. SB never gets triggered.
Yet another wrinkle comes with the issue of the same effect triggering multiple times as damage gets bounced around. If each time damage is redirected, triggers can occur and there is no exclusion for already triggered effects, then you could get a situation where heroes are tied for HP and SB triggers endlessly. If you don’t allow triggers on redirect then Superhuman Durability wouldn’t seem to trigger after LftF.
There are other ways of handling it and scenarios, but that should be enough to induce headaches.