did not brown bacon slices long enough

Pamela, the bacon slices are not going to keep their crispness because they will soak up the broth. As Beth said though, you will still get the nice bacony flavor in your soup. I think trying to re-fry the bacon will be frustrating (and messy!) because of the broth in them. I often sauté chopped bacon right in the soup pot with firm vegetables (carrots, celery, potatoes) until they soften, then add the broth to that.
If you want a crunchy garnish, best to sauté some fresh bacon.

You could brown some more to your desired texture and then use it as a garnish. You will still have the flavor from the original bacon and the crunch from the garnish. I have a clam chowder recipe that calls for browned bacon. The veggies are sautéed in the fat and the bacon goes on top of the finished product.

I wonder if you can strain them out, rinse off with water and try to sauté? It's worth a shot. If they are crunchy use them to garnish, if they are stiff squishy at least the flavour is in your soup already.