Disappointment is what one experiences when one’s expectation is not met. So, as an initial matter, if you have no expectation (about the outcome of a particular circumstance), then you can not be disappointed, no matter the outcome.
Disappointment is not the same things as sadness: If you expect your house to be blown down by a hurricane, for instance, you can be sad when exactly that happens (because you will have to live in a motel for a while, perhaps)—but you can not be disappointed. Just the opposite, for your expectation will have been fully met. To the contrary, if your house remains standing when the hurricane has passed, you will (presumably) be glad, but you should feel disappointment. And there’s no reason to feel bad about that.
Definally. 
Isn’t “disappointment” what one experiences when one’s POSITIVE expectations are not met? I think “relief” is what one experiences when NEGATIVE expectations are not met.
In fact, Kate, no. For who is to say what is a “positive” expectation?* One man’s positive expectation might be another woman’s negative expectation, and if we start mucking about with connotations, then all is lost.
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*Definally. is to say, perhaps, but another time.