Most vegans will say "do whatever you have to do to live" and want a reduction in the consumption of animal products and harm of animals wherever possible. They will, for example, take vaccinations and medical treatments that have been derived from animal products if there are no alternatives.

So, if a person has honestly tried everything and they absolutely need to eat some meat and fish to be healthy, then most won't have an issue with it. There will always be crazy internet kooks though.