Mostly old and poorly educated vote for Brexit -> UK leaves EU -> skilled EU citizens with no personal commitments to UK (family, spouse, wanting to not return to previous country anyway) will leave including doctors, nurses, and elderly care staff -> NHS struggles -> care homes struggle -> old people die off faster -> ratio of young to old voters rebalances -> in 20 years time vote to rejoin EU -> rejoins EU.
Don't worry, Brexit is a self-fixing problem.
Mostly old and poorly educated vote for Brexit -> UK leaves EU -> skilled EU citizens with no personal commitments to UK (family, spouse, wanting to not return to previous country anyway) will leave including doctors, nurses, and elderly care staff -> NHS struggles -> care homes struggle -> old people die off faster -> ratio of young to old voters rebalances -> in 20 years time vote to rejoin EU -> rejoins EU.