Some slugs and snails do die after laying eggs because they can lose weight after laying eggs.
Not all slugs or snails die after laying eggs though as some go on to live their life and care for the baby slugs until they are ready to be on their own.
Slugs may then go on to have more baby slugs but in rare cases some slugs do die after giving birth to baby slugs.
Some slugs lay single eggs while some slugs can lay eggs in clutches of 50 or so and can lay up to 500 eggs per year depending on the species of the slug.
Just like humans and dogs and other animals can die as a result of birth slugs can as well but it's rare that they do die as a result of laying eggs.