If properly maintained, a trademark registration may exist indefinitely provided it is continuously being using in commerce in association with the claimed goods and/or services it covers. Trademarks are assumed to be abandoned after three years of consecutive non-use or excusable non-use, but this may be rebutted under certain circumstances.
A trademark can be lost it becomes generic term for the goods and/or services it is associated with instead of operating as an identifier of the source of those goods and/or services. In the trademark world this is known as genericide. Effectively, genericide occurs when a mark becomes so closely identified with the goods or services to which it is associated that its consumers associates the mark with the goods and/or services themselves. While this process is relatively rare, it is an interesting problem because it means that brand recognition efforts have been so successful that the brand becomes inexorably tied to the product, and the product becomes identified by that brand mark. Notable examples or trademarks that have become generic include Thermos, Escalator, Kerosene, Aspirin, Yoyo, and Frisbee; all of these are marks that were used as a source identifier first, but have become so tied to the product that they are now associated with the product itself rather than the brand.
An interesting example along these lines is Google, which changed its name to Alphabet. The company name “Google” was becoming generic for an internet search, raising the potential threat of genericide. To mitigate the risk of genericide, many companies operate on the principle that a trademark should always be an adjective rather than a noun or a verb. Once a trademark starts becoming generic in the consumer base, some companies, like Xerox, have launched media campaigns designed to remind the public that the mark is a trademark, not the product itself.