Note that the guppies would have died anyway without treatment. So would have the fry.

I have been wondering about an aged guppy female I was given. She never did drop (rats!), has obviously been aging beyond whem she could have fry and has had her own small tank for months. I toyed with the idea of putting her in a jar with a little dissolved clove oil and anesthetizing her. Evidently a little drinking alcohol is needed to dissolve the clove oil and that is the more often recommended approach these days, though a quick blow to the head (unpalatable for many folks) or leaving the tank out on a very cold night is still ok by Terry Fairfield.

I kept her and even fed her live food the evening before she died Saturday. Her's was such a gorgeous strain (red delta and red-albino delta), that is why I took her in. I do regret that she never dropped.

If your guppy fry were with the adults when they were treated, they should be fine. They probably had tiny, larval Camallanus within them and those should have been successfully treated. You may find fry hard to give away. Most people prefer that you do the work of raising them to a more attractive stage. ;)

If you can do a near tear-down and keep the fry in the tank, they should thrive. (Or tear the tank down, keep the gravel wet and return the fry with some treated, seasoned water. Feed lightly at first. A few growing plants will absorb most ammonia given off by a few fry.) Just add as nearly as much treated and seasoned water as is in there each day or two until it is full. I know that doesn't do your HOB filter much good. Just rinse it out and leave it for now.

And while fry are not nearly as interesting by themselves as adult guppies, they would thrive in a larger aquarium than we many times give them. And there is a wonder in watching them mature.