When is it time to pull a plant?

[LMinAL]

I'm a newbie here! Second year of gardening. My tomatoes have septoria and bacterial speck as confirmed by my ag extension diagnostic center. I've been snipping affected foliage, applying bleach spray then alternating with Daconil and copper. The septoria seems to be better contained by Daconil, but the speck only responds to copper. Some plants are tolerating the loss better than others. The past few days have been terrible with constant rain and I haven't been able to keep preventative on them, only applications of bleach between showers. The leaves are getting fewer and further between as both diseases are spreading like wildfire.

I was wondering how much foliage does a plant need to ripen tomatoes? Some plants have 1/3 of their foliage left, but I'm down to 1/4 or less on a couple of plants. All have fruit that hasn't ripened. If it ever stops raining I'm going to put shade cloth up to prevent sun scald. It's sad to watch them slowly dying. I just wonder if its in vain and I should pull the plug on the worst of them and concentrate on the hybrids which are holding up a little better. So sad for my heirlooms - they're my favorites.