There are some workers who have healthcare benefits that continue after retirement. A good example is the auto workers. But the overwhelming majority of us do not, and as you say, will be totally dependent on medicare for health insurance in our retirement years.
Even the retired auto workers use medicare - they may get supplemental insurance from private insurers as a retirement benefit, however.
There is no alternative under the law - all seniors age 65+ MUST enroll in medicare. Period.