When I leave my employer do I get a confirmation from the tax authorities that the 30% ruling ends?
I had the 30% ruling granted since 2016, but I quit the company at the end of August 2019 and since then I have been living spending my savings. But so far I have not received any letter from the Tax office that my 30% ruling was taken away.
That is right. The ruling is granted for the period you are working for the employer with whom the application was filed, with a maximum of 5 years or less due to previous stay in the Netherlands. This is specifically stated on the declaration which was issued by the tax authorities when the ruling was granted to you.
This means that the moment that the contract with your employer ends, automatically the 30% ruling ends. This is not confirmed (in writing) by the tax authorities, so it is correct that you did not receive a letter from the tax authorities about it. If you sign a new contract with an employer within 3 months again you can apply for the 30% ruling again, otherwise you will lose it permanently (unless you leave the Netherlands for 25 years).
From the day the 30% ruling ends you will be treated as a local resident and will have to declare your world wide income (including your savings and investments).