With little thought to it and even if the key has enough counterweight, there is a risk. You see, the drinking goes slowly. If you little by little drink it the bottle approaches the weight balance point with counterweight. It can end up the drink being higher than your head and neither side moving anywhere... just a word of warning At that point you may be able to try to jump up and bump the can up with your head to get key lower. All depends on how well the rope moves etc.
It seems to me that the answer is to make sure that the length of the string is such that at the halfway point, both key and straw are reachable.
A less reliable alternative would be to have a loose end on the the string to the can, which can be grabbed to pull it back within reach should it fail to achieve sufficient altitude.
Yet another approach would be to have an extra weight attached to the key, but supported in such a way that if the drink had ascended too far, the key's weight would pull the second weight off its perch, safely tipping the balance in favour of the key. That would need to be tested thoroughly.
In any case, the best precaution in any scenario attempted for the first time is to perform an unbound dry run, to get everything just right. Rushing headlong into a scenario, without having learned the engineering details of it, is a mistake.
Sometimes a little detail that only shows up in the actual execution of the scenario can turn an otherwise pleasurable session of self-bondage into an unpleasant and even frightening experience.
Jenny.
Helplessness is a doorway to the innermost reaches of the soul.
If my corset isn't tight, it just isn't right!
Kink is the spice of life!
Come to the Dark Side - we have cookies!
If in doubt, try it out...
I think once the drink is light enough to start rising, and there is not too much drag in the lines, the drink should go all the way up and the key (and weight) should come all the way down. I would not think it would act like a balance scale and stop mid way just because the weights are equal.
An easy way to test this is set it up, just sit there in front of the drink container and slowly sip from it until it takes off and see what it does...
Of course what you could do, just to make thinks interesting, is get secured like you would do the scenario, but have your spare key under the drink bucket. And the rule is: you can't get free by pushing the bucket out of the way...
That way, if it does fail, your key is right there...
Or, you can add a board with a small magnet attached, assuming you use a metal bucket, that way, the magnet will add additional weigh until it's force is overcome, the it should shoot up and the key come down. Provided the strength of the magnet is less that the key weight...
Now, after you do this, report back the results, there have been several questions on this, and no one has provided a tested answer...
You could set this up with an electromagnet so that you cannot get out before a set time, regardless of how much you drink.
At that point you may be able to try to jump up and bump the can up with your head to get key lower. All depends on how well the rope moves etc.
