The trick is to put tweezers, flathead screw driver, something behind the tab and pull it out, take a knife and cut 1/4" off the tab and stick it back in. It will continue printing the last bit of ink.
If you let it keep printing, two things can happen.
#1. If you cut the tab perfectly, it will stop and tell you that you are out of ink when it's fully dry.
#2. If you tab too much, it'll dry out the lines and it's a pain to pump back in.
However start with a 1/8" cut to be safe, you will get used to it. I've printed two 4' X 8' banners after cutting the tab, then changed inks and everything worked perfectly still. So you can get quite a bit more out of them. Roland stops it early to ensure you don't run it dry, but there is still 10% or so left in it. Get 7% or so out of it, then throw it away. You can also pause the printer and swap inks as well, so if you feel it's been printing too long or you forgot to change it, that works.