Severus survived, moved abroad in a muggle neighborhood and wrote 7 "Potions for Dunderheads" books, one for each year he taught at Hogwarts, using his own recipes.
He put wayyyyyy too much indications on every steps : color, potential dangers (risk of irritation, toxicity, etc), developed a mortality /100 scale for each step, indicate the margin of safety (3 more or less drops and you're 3rd degree burned dunderhead) .
By the seventh book, he learned biochemistry and organic chemistry, and added the pH, reaction equations, active ingredient, what protections to use (gloves, glasses) and progress tables.
Then he wrote "Muggle Techniques Applied to Magical Potions", in which he explains how to take off your gloves in safety, how to sterilize the supplies (including dragon leather gloves), when and how to use an autoclave, a centrifuge, and everything you can find in a muggle lab.
Through the years, he wrote many books :
Fresh, Dried, Fermented or Chopped : a proper use of plants in magical potions ;
Raw, Rare, Blue, Well done or Burnt: a proper use of animal parts in magical potions ;
Healing Spells and Potions for Daily Life ;
Why Using Your Wand While Brewing is the WORST IDEA EVER ;
You Blow Your Cauldron : Healing Spells for Dunderheads
Ancient Runes and Alchemy: How to Make the Lab Dunderhead-Proof
Starry Sky and Unicorn Poop : Potions for Toddlers and Children (under a pen name)
Easy Peasy, Potions Easy (under a pen name)
Those Legal Potions That Should Be Worst a Dementor Kiss (very controversial, includes Amortentia)
He also published many papers in potions magazines, all controversial, and that's how the word "Snience" started to spread.
He has been offered many jobs in potion labs, but never accepted it. However, he agreed to teach some summer camps when he's short of money, where he met very skilled wizards in herbology, magical creatures, spells and alchemy, whom he befriended.
They called themselves The Mad Snientists Team, since they all started to use muggle knowledge to improve their research.
And then, from above, he watches the first prom of students of the Severus Snape Magical Institute for Very Skilled Witches and Wizards attend their first class.
