If for example I am in the middle of an order with a customer, and they happen to close down their account or their account gets terminated for some reason, what happens at that point exactly? Would I still get the money or does the money go back to the customers bank/ paypal or whatever?
Nope, you won’t get paid. The order will get cancelled, since once there’s no existing buyer, no longer the order will be possible to be delivered.
In such a case, Fiverr will notify you of the cancellation, and you should contact CS to ask them to kindly take care of it so to not affect your stats.