There's a lot more to health than nutrition
- Stress management
- Sleep
- Genetic / Epigenetic considerations
Regarding DHA deficiencies, it isn't a foregone conclusion that vegans or vegetarians in general will be deficient - perhaps not optimal
- http://www.nutraingredients-usa.com/Research/Omega-3-ALA-intakes-enough-for-EPA-DPA-levels-for-non-fish-eaters/?c=PlxCReLmonDO4Z3AQO7Luw%3D%3D&utm_source=newsletter_daily&utm_medium=email&utm_campaign=Newsletter+Daily
- http://evolutionarypsychiatry.blogspot.com/2012/01/just-eat-fish.html
In spite of being a vegetarian Paleo, I firmly believe that eating well-sourced animal products will maximize your chances for health. But YMMV! Do what works for you based on the scientific evidence you have before you and validate your n=1 experience FTW!
EDIT - to answer your question, yes it is "possible", but if health rather than ethical considerations is your objective, it does not seem "probable"
