*IF* you drink enough to make a drink package worth it, the amount you pay in tips is the same is my point. I think, at least on RCI, the number of drinks to break even on a package is 4-5 every day (not sure on this, worth double checking).
The tip doesn't make enough of a difference to change the math. For whatever your drink of choice (alcohol, non-alcohol, soda):
A) What's the cost of the package per day?
B) How many of those drinks would you realistically get each day?
C) What's the ala carte cost of the drinks?
Multiply B & C. Is it more, less or about the same as A? THAT'S how you decide whether or not to get the drink package.
Also keep in mind, the package average is EVERY day. If you're on a port intensive cruise, and off the ship for eight hours/day, that cuts down on the number of drinks you'd consume. You need to factor that in.
Royal Caribbean's official stance is everyone over 21 in a cabin needs to purchase an alcohol package if one person does. But there's a LOT of folks on Cruise Critic who say they've been able to get a refreshment (non-alcoholic) package along with an alcohol package if they called to order them. I've only heard one person say this didn't work for them.