I am curious what the chances are the heads don't work properly after even if it is put away properly?6 moths is a rough amount of time for a printer to sit like that. You could risk it and just keep it plugged in but most likely will have a fight on your hands to get the head firing again when you get back. Also, if anything gets jammed or an error occurs, the machine could pause with the heads uncapped and then they will just completely clog. The proper way to do it would be to empty the machine of ink, flush with cleaning solution and re-fill when you get back.
I am curious what the chances are the heads don't work properly after even if it is put away properly?
If you are 100% sure all the ink was flushed out then you should be able to fill it back up without fail every time. Usually when it fails it's because people don't check the lines after to make sure the flushing process actually worked. Sometimes 1 line might just not flush properly and you have to manually finish it off. There is a very small chance that the heads get damaged during the manufacturer's flushing process but the chances are higher when you manually flush it with a syringe.