'Boss claims that me quitting will result in the business closing': Worker gives 2-week-notice after basically running the company they work for for their boss, prompting boss's total meltdown

It is truly mind-boggling how some employers will treat the workers who are essential to the success and operation of their business. They gamble that they can pay them below market rates and keep them exactly where they are and that their workers will continue to be milked like the cash cow that they are… After taking on increasing responsibility in their boss's small business, this worker knew it was time to move on to greener pastures. They did what they thought was the right thing and gave their boss their two-week notice, prompting a meltdown that they could not have anticipated. 

As commenters in the original thread noted, this begs so many questions. Like, if they were so important to the business why didn't their boss recognize that and reward them for it? Surely, there were chances and opportunities for their boss to give them a promotion or even a partnership in the business that they were so essential to. Still, their boss's general laissez-faire attitude and seeming reluctance to lift a finger to support their own business has spelled their own doom. It seems that they were totally complacent and happy to let the employee do all the work while they raked in all the profits.