To give you a direct answer to your question.
It is not possible for the ordinary fishkeeper to disect you guppy to save the fry. The reason for this is you would need to cut through the peritonaeum. This is a very delicate membrane and you would need to have a surgical scalpel to perform this operation. You would also need a set of neuro opthamic lenses to see what you are doing. Then, the dead fish would need to be operated on within minutes of death, as immediate asphyxiation begins on the fry at onset of death of the host. If you then have a steady enough hand and a team to hold the fish whilst to cut through the fine membrane and if you don't damage the fry with the tip of the scalpal blade or puncture the gut, you may be lucky to save a few.
It is a specialist job and normally reserved for larger fish such as sturgeons.