I think kakaroto is assuming that the restaurant will always be unable to buy food in Bitcoins. Whether that assumption can be made is debatable.
I think that assumption is the key. If the whole chain, from raw material to manufactured materials... with absolutely widespread usage, if you can get literally anything with bitcoins, it would be another game.
But as long as you can't pay electricity, gas, water, employees and supplies with bitcoins it would be a gamble.
I guess that the most important thing is the EVENTUAL widespread adoption, but if it fails to attract new adopters and yet sales goes up at this restaurant, it would drop the price severely.
There are two ways of getting bitcoins: by mining or buying.
If you bought and used them, it would balance it, so we would be fine.
But if you farmed it, it would make it drop.
If you bought bitcoins in the past, and now you are spending your savings (just to try out the novelty), and not planning to buy more at this time, it would make it drop too.
Therefore the only hope is that by getting adopted by a high profile business is that:
1) It will cause some awareness, and entice new people to adopt bitcoins, causing them to buy bitcoins (hopefully)
2) Eventually other businesses could jump in and eventually the whole economy will be hopefully self-sustaining with bitcoins. (Very long shot, finger crossed, god willing)
And if these two things don't happen, then bitcoins would be doomed.