hello friend, I think you have already given yourself a good answer! collect what little remains if you judge that the plant is dying soon, at least you will have something to smoke while you put in a new seed ;).
for the future I recommend constant prevention (until flowering) directly on the leaves, with neem oil and a few drops of potassium soap to emulsify.
also remember to thoroughly clean the box with a water-bleach solution, or other disinfectant solution that can kill parasites.
bye bro!