Even if this petition accumulates hundreds of thousands of signatures, what should happen? The sale has been announced, which means that, but for regulatory approval (if any), it is done: The owners of LastPass have agreed to terms and have signed contracts indicating this, contracts that are binding.
Were they to change their minds LogMeIn could in all likelihood sue both LastPass and the owners of LastPass, personally and severally, for breach of contract and for a number of other things.
No government will interfere either, as few if any governments will assert that they know both a business's business and the needs of that business's customers better than the business itself - not to mention because of the precedent it could set and uncertainty it could engender.
The best response of concerned customers is one, research, and two, should the research so indicate, voting with their feet and either saying put or moving to another service.