Hello there!
I know how to find out whether LOS exists when an attack goes straight through the line between two hexes.
What I don't know is – what happens if an attacker picks a target, but the defender then chooses a side which makes him not in the LOS?
Does the attacker simply not get to attack anything (because he has already declared a target, except he can't hit it)?
Or does the attacker get to pick a different target (because in order to attack, LOS is required)?
The rules left me feeling ambivalent as the example on p. 101/102 of TW seems to suggest no other attacks than the ones with explicitly established LOS are resolved, but it doesn't clarify whether that means just in the context of the particular scenario (i.e. with no other potential targets present) or whether it means overall, generally speaking, and the attacker is out of luck. Neither do the LOS/combat rules fill me with 100% confidence, as in one place, LOS seems to be established after picking a target (and thus seemingly locking the attacker out of picking another one) while at the same time elsewhere, attacking seems to be subsequent to & dependent on successfully establishing LOS.
(As a sidenote, we have always ruled that you check LOS first and if you have none, you pick a valid target instead, but a recent discussion together with the slight uncertainty in the RAW made us dig deeper into this confusing hole...)
