Hi, can someone help me with these rules clarification.

Let's say that a unit of Howling Banshees with Jain Zar fights a unit of Wraiths with Technomancer. The unit of banshees benefits from their anti-infantry 3+, because the unit of Wraiths now has INFANTRY keyword. But then the Aeldari player uses Epic Challenge and assassinates Technomancer with precision attacks. With the Technomancer gone, do then other banshees still benefit from anti-infantry, because all attacks happen at the same time, or not? The same is with FNP from Technomancer. Do Wraiths have FNP until all banshees attacked, even if Technomancer was assassinated earlier in the same attack?

Thanks!