@Clitheroe: Funny thing with printers is that it uses ink for cleaning, which is why it's needed. Regardless, if you keep empty cartridge in place, it should work just fine at least for while. Unless HP became even bigger dicks lately.

A lot of HP printer (for a long time now) have it so that if ANY cartridge runs out, it stops working completely and says something to the effect of "oh no! you've run out of one color, please buy more to continue printing!!!". Yeah.