Last Stand states
'before removing that unit', so this is clearly within the attack sequence, which Surge Forth is not.
It can also occur, triggered by the unit's destruction and therefore death, at several points within the attack action:
- immediately after a hit and/or wound allocation resulting from the attack die roll (step 6 of the attack resolution, RB p.17, see below), in which case the unit dies after performing it's retaliatory melee attack action but before the now unnecessary panic test;
- immediately after an attack effect allocates automatic wounds before or after the die roll (out of my depth here, I ken not all the potential cards listing such an effect) which would result in the unit's destruction;
- immediately after a wound allocation resulting from a panic test die roll (step 7 of the attack resolution), in which case the unit dies similarly after performing it's retaliatory melee attack action but before the attack action itself gets completed (step 8 of the attack resolution);
So, in the case of the unit actually dying from an attack action (and not some other non-attack-related effect), 4. is out the picture, so are 3. and 2. since they'd rest on
'when this attack is completed' which is not the case if one follows the attack resolution steps. 1. is a bit problematic in the terminology, not knowing if you mean the attack roll or the attack action.
For reference: