Sentence:  It would be even more valuable because that same aircraft could immediately destroy any targets it discovered - no need to wait for a missile to come all the way from the United States with the chance that the target , if it were mobile , would <WSD>be</WSD> gone . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)