There are not actually a large # of insurance actuaries. What will greatly reduce employment across many industries is AI. There are already companies where workers are under the "management" of AI, not managers. As more companies codify their internal information practices into data streams, fewer people are needed.
Those that are left must have specialized tech skills. Data management will move down the organization to produce real-time feedback.
The insurance employees who "deny" coverage are not actuaries. They are underwriters whose work is overseen by a corporate Medical Director. Yes, a doctor - and a very, very highly paid one. The CMD is the one who highlights any changes in claim statistics to the CEO and Board of Directors. If a lawsuit is filed against the insurer, the CMD is the one who reviews the policy's original medical underwriting with management and the legal team.
I agree that healthcare will go to a "Medicaid for all" system. Basic healthcare goes a long way to improving all of society - think vaccinations, diabetes, high cholesterol, etc.
A combination of private insurance and government coverage probably works best, at least in the short- to medium-term. Neither one can pay for everything. People will still need to evaluate their own risk profiles and decide what coverage to buy.
The current US system of tying healthcare to jobs - and only certain jobs - is inefficient and simply cannot be made workable.