can i just farm up the materials for irisveil and save them after the event or will they all disappear after the event ends?
Most event items disappear after the event ends, though most event items act as currencies to be used in the event shop.
The items you are talking about are probably the ascension materials for Irisviel. Those won't disappear after the event, so you will have time to level her up later.
materials, exp, and anything else that has any value outside of the event stays forever. But event currencies go away (they have no use outside of the event anyway)
I recommend to you to save exp cards form the lottery box to ascend her 2 stage, you gonna need that for the event.
