Honestly if they really, really wanted to make this impactful they should look to Guild Wars 2 Lions Arch event. Put basically what would happen is a series of events that lead up to something big (over the course of a month or two). The final event leads to the tower being invaded and the guardians being displaced/pushed out to a new zone which is basically a refugee camp in the city, from there players have to work together to retake the tower, naturally they are successful but it's left heavily damaged from the battle leading to the map having slight adjustments like destroyed architecture etc. which gradually gets repaired/fixed over the duration of a month. If you did a Invasion that you wanted to catch everyone's immediate attention that's how I would do it and changing the default spawn point of the tower to the refugee camp so new players don't get lynched on arrival.