For the quilt, you would have to baste closely all around the edges if you want to try to get the stain out before continuing the quilting. It is probably preferable to finish the quilting first.
For the stain removal, I would probably try RetroClean first (
http://www.retroclean.com ). If that isn't enough, then I would try soaking it in a top-loading washing machine for a day in powdered, colorfast bleach. If that still doesn't do it, I would use Synthrapol in hot water in the washing machine -- several times.
I have never been successful in removing dots of mildew from fabric, but here is a website of tips:
http://home.howstuffworks.com/how-to...ew-stains2.htm
By oxygen bleach, I think they mean Oxyclean.