Also, about Bill attacking both soul and mind, while true... is there evidence he can do the same as UT characters who can indeed attack soul and body at the same time? Because we don't assume everytime a Dragon Ball character kills someone, they destroy their soul as well.
And this leads me to think that... can Bill attack before Asriel uses his Info 2 EE? Chara needs a slash, but Asriel seems to be better at manipulating the game world, as as Photoshop Flowey he already did a lot of funny stuff with thoughts, so Asriel being able to delete the game world with a thought does not seem far fetched, especially when he does that passively in his FP state.
Aka... Asriel stomps, as he thinks and Bill is erased.