There are three relevant rulings:
CoE 6 wrote:If an Assassin targets Bilbo at Bag-End and Farmer Maggot carts his butt off to the Old Forest, all attacks of the Assassin are effectively cancelled and the Assassin is discarded, even though the same Assassin is keyable to Old Forest (i.e. the Assassin is sort of "keyed" to Bag End when he attacks there) correct??
*** The remaining attacks of the assassin are not rekeyable to the border-hold of Old Forest. The remaining attacks are discarded without effect, but not cancelled. The attack is still considered faced.
CoE 19 wrote:If my company "teleports" using Farmer Maggot against an assassin's attack, what happens with the two remaining attacks ?
*** They fizzle.
CoE 58 wrote:So, Farmer Maggot vs. Unabated in Malice (card text below): Galdor is at the Barrow-downs on which an Unabated in Malice is played. Farmer Maggot is in play. Galdor goes in, faces the attack and instead of fighting it he lets Farmer Maggot take him to Old Forest. Farmer Maggot states the attack is now cancelled. Unabated in Malice states in return that the first attempt to cancel the attack instead cancel the Unabated. So ( In My Hysterical Opinion ) Galdor finds himself still facing the 1@8 Undead attack. Is this correct?
*** That is correct, though the movement effect of Farmer Maggot still resolves successfully. Consider it a parting shot by the Barrow-wights.
I think that we have an implicit contradiction between 6 & 19 on the one hand and 58 on the other. Either:
(1) you should have to face all attacks of the assassin and face the "parting blow" of the barrow wight, or
(2) you shouldn't have to face the 2nd and 3rd attacks of the assassin or the "parting blow".
My inclination is towards (1). Note that this ruling should extend to a few other cases: (a) 1 attack of a Nameless Thing has been faced and then Doors of Night is removed from play; (b) Slayer vs. Farmer Maggot; (c) Slayer/Assassin vs. Gloom's second effect; (d) Farmer Maggot vs. minion Bag End; etc.