They won't die off.....
This is the odd time I would say to flush - only once......
Your main problem is TO MUCH P, to early! The plant shows "classic" over use of bloom "foods"! NO amount of added N will fix this!
You also have low Ca/Mg
Your pH problem comes from the abuse of the bloom foods......
So then, Flush with 2x the pot size in water (water should contain a Ca/Mg supplement and a "zyme" product in the last gallon to be poured through) All of the flush solution should be pH'ed to 6.5.....
When the plant has dried out enough to water again,,,use a feed with an NPK of "around" 2-7-9 or 2-6-8.....the K can be lower......Do not add any high P additives - period...to this grow!
They will finish out ok...they will not reach their total potential.....