Just about every line now uses a cabin roll call at the drill, and cabin stewards are checking cabins while the drill is going on. Thats not to say that you can't figure out a way to hide out BUT even though the drills are pretty much the same the procedure does vary from line to line, even ship to ship due to different layouts and IF there were a fire on board and rooms and hallways were filled with smoke it sure would be nice to already know where you needed to be rather than trying to figure it out at the last minute.
As far as what they do about it, all that don't make it to the drill, will be contacted and there is usually a special drill for them, plus you have to walk around in you life vest during your special drill so everybody knows you tried to sneaker out of the real drill and got caught, those with no sense of humor usually laugh and point fingers at you.
Go, get it over with, then start enjoying your cruise, a small price to pay for not being the cause of your own or somebody elses injury or fatality because you didn't know what to do.