This sounds like a home-brew Note. There might be all kinds of wrinkles, some good for you and some not. If there is substantial money involved, yours personally, it seems worthwhile to have a MD attorney look at it and analyze all the consequences. It will likely cost you less than you think.
Licensed in Maryland with offices in Maryland and Oregon. Information here is general, does not create a lawyer-client relationship, and is not a substitute for consulting with an experienced attorney on the specifics of your situation.
It really depends on how Company X turned into Company Y. I'd have to know more about them and the transaction between them, and read the language in the Promissory Note. If X sold the business to Y and then dissolved, you might be off the hook. But if X just changed its name, or if it merged into Y, probably not.
The thing is, the right to get paid money (in this case by you, under the Note) is *valuable*. I'd be surprised if the owner of Y allowed a deal that lets you off the hook. There's no such thing as a free lunch.
The answer is in the details of the Note, and the documents relating to Company X and Company Y. A mere change of name, evidenced by a filing with the Department of Assessments and Taxation, does not terminate corporate existence.