Having had personal experience of how Insurance companies in Thailand will use every loophole to avoid paying, I doubt that they would miss an opportunity like this to shaft their customers.

This isn't a Thai thing its worldwide!!

But in "most" of the rest of the world, you at least get a semi fair chance to argue your point.

My legal adviser was told by the company to tell me to take it further if I wanted my money.
I was advised that this meant legal action which I was assured would cost me at least double what my claim was and that I would not be allowed to claim my expenses when I won.

Basically I had a choice .... lose B50,000 or lose B100,000 plus and win? the B50,000 that I was owed

But in "most" of the rest of the world, you at least get a semi fair chance to argue your point.

Not in my experience! Insurance companies are as far down the list as 2nd hand car dealers and estate agents.
That said I have found the car insurance here to be spot on compared with the UK, no arguments, agent visits the scene, deals with the police and he does all the spade work you just claim.

As I'm booked to fly back to BKK in July I emailed my Travel Insurers (Insure&Go in the UK) to see how I stood.
If I had been in Thailand already I would be OK as long as my claim had nothing to do with the Coup, BUT as I have not set off yet the insurance is TOTALLY NULL AND VOID, even for a bag lost in transit.
So, I guess the only way to be sure is to check it out direct with your insurers and not trust in what others may post.

My dad recently went on disability and his employer is wanting to cancel his medical insurance he had through them. Can they do this?

They may well be able to unless it is written into his contract that they will continue with the policy after he has left their service.
One way may be for him to contact the insurance company direct and explain the situation, asking them if he can continue under his own name.