sadly that is true... there is no going back. I wish there was though... like maybe a mission where you go back in time with your lv 20 infused ascended 15k armor wearing bad ass self and go destroy all the charr at the searing pot. Now I know you can kill all the charr at the pot pre-searing but it doesn't stop the searing from happening. But if they removed that ability and did it as an actual mission... Come on Anet that would be awsome!
if you want seeds run the tengu farm run theres 3 plant type mobs ( monster or beasts) at the end of the 4th patrol that always drop plant fibers/seeds