Let's say the vast majority of jobs get automated. Why not continue to pay the former employee his check? The robot doesn't pay bills?

You have the right idea, that automation should decrease the amount that each human needs to work for the same pay, instead of only profiting the company owners.

But why do you say companies would make more money by paying for robots and electricity to run the robots while also paying the employee salaries?

And what about the next generation of humans? Paying former employees a pension is one thing, but do your descendants go on paying their descendants forever? Will grandchildren of high earners get higher pay than grandchildren of minimum wage earners?

There are three ways to deal with automation. One is to pay workers a living wage for fewer hours of work, similar to what you suggested but with some actual work still involved (though in different jobs, such as programming the robots). This would allow everybody to remain employed part time instead of fighting over the dwindling supply of full-time jobs.

Another approach is to tax the profits from automation and use that money to pay for everyone's living expenses. When the money is distributed only to the people without income, it is called welfare. When distributed equally to all citizens it is called Universal Basic Income.

And the third approach is for the former workers to own the company and thus get the profits directly. This is communism in its original form: Marx predicted that when workers were not paid enough to live on, they would seize ownership by force rather than starve.

Europe has mostly chosen the second approach. America is on track for the third.

The company would lose money, because the robot costs money and repairing and maintaining it costs money.

Because a competitor would start up without ever having those employees and only having automation.  That means their costs are much lower which means they can sell their products for much less than your company who is paying employees to do nothing.  The end result is nobody buys from your company at the higher prices and you go out of business.  

The reason the employee got replaced by  a machine is that he cost too much.  The cost of employees is about 150% of what their wages are.  The robots cost a lot of money but are more reasonable than human beings. 

Businesses are not charities it makes zero since to pay former employees for not working

Why should they pay you when they can keep it for themselves and get rich? These are your “woke” companies promoting social justice by the way. Creating a new underclass for the rest of us to enjoy.