The Modern "Victory Garden"

I've been meaning to ask this for awhile now.  I have chard plants that I was planning to overwinter and possible bring in the house but they have now got mildew.  I cut all the leaves back and sprayed with sulpher but it came back.  Is it safe to eat the leaves?  I'm guessing not. 

Anything I can do about it?

I think it would be perfectly fine to eat the new leaves that do not have the infection.   I have never dealt with exactly this situation but if it were me, I would eat it!   If you had any doubts,  just use it in cooked dishes rather than as raw salad material.