When my tomatoes start to get blight, often I pick them all off at once.
Any, whether ripe or not, that have the brownish black on them are discarded straight away, the rest are washed and dried and laid out on trays.
If they are ripe, I use them.
If they are green and dull, I discard them as they don't really seem to ripen properly.
If they are green and shiny and a good size, I keep them to ripen.
They all need checking daily to see if any are starting to go brown with the blight, but usually I manage to save a fair few, it seems to me to be well worth doing.