It has been viewed many times that "plans" that are spoken about during the political season, change dramatically once they get into office. If you look at the past "plans" or basically the verbiage used while on the campaign trail, the final outcome of the "plan" is typically changed. Both parties need to agree and other aspects come into play, there is no visible sign that shows the health care will be taken from millions of Americans.
Bernie Sanders is all about free health care and free college. In fact, his whole platform is so based on offering free things to the community that some have labeled him a communist or socialist. Bernie Sanders believes that the answer to all of our economic problems lies in higher education and affordable/free health care.
I think Sanders wants everyone to have free health care. I don't think this is taking care health care from millions of Americans. I don't think free health care is a good plan, but I also don't think it will take health care away. Sanders is a socialist and he wants everything for free.
A large criticism of the expansion of Medicare is that also millions more Americans are insured, the quality of this insurance is minimal. Bernie Sanders wants to make health care not only more available, but also more equal. Private insurance companies will only be in existence for supplements to the single payer health program, ensuring that all Americans have access to the same quality of health care, rather than people being turned down from high quality facilities because only private insurances are accepted.