demand for milk is not all that flexible, because there is no direct substitute for milk, with all the calcium and stuff; also, milk might be subsidized/regulated - it is in the EU, which skews the prices, etc., etc.).
There's many substitutes for milk, actually. Beyond direct stuff like soy milk, pretty much any other liquid counts, and calcium requirements shift into other substances. Remember that the majority of the human race is still lactose intolerant. Milk's not a very vital substance, really.
But generally, if the demand shifts from milk to something else, there _is_ net economic loss.
Fulfillment of wants shifting into something else isn't a net economic loss -- a net economic loss requires the money involved to disappear into the aether or not get used (i.e. not spent or invested), which is fairly rare in an even remotely healthy economy. Less money spent on milk means more money spent on something else the person would want, not less money spent overall.
With minimum wage set higher, there will be more thing that just won't be done. Less people will use some of the services, as they will become more expensive, and workers who granted those services will be laid off; there is no going around that, plain and simple.
And, assuming something doesn't go wrong, they'll find work in the new services that come in to demand. Demand usually has significantly more effect on job availability than supply when there isn't an absolute physical bottleneck, and companies not wanting to make less profit isn't one of those. People
will be laid off, but that doesn't mean the net work demand is going to decrease, because people are still going to want stuff, even if it's different stuff, and we still need people to get that done (for now).
If the fast-food joint needs one worker and earns, say, 30$ an hour above the cost of resources, than as soon as minimum wage is above 30$, the joint closes and there is now 0 workers needed.
Sometimes. Sometimes they keep going, at times for a significantly long period -- it's not uncommon for companies in the red to operate for quite a while just to mitigate the relative price of fixed expenses. More often something gets rejiggered (usually those resource costs). And the joint closing isn't necessarily a bad thing, in the long run -- something else will pop up, if it's not already there.
That said, you do generally try to rig these things where an increase in minimum wage isn't going to cause businesses to become absolutely unprofitable. Fortunately, most of them (yes, including small businesses) have pretty significant wiggle room when it comes to wages, particularly for their lowest paid workers.