2. If the new company declares (with documents) that after the merger, it will re-establish the labor relations, recalculate the length of service and re-sign the labor contract, then you should terminate the labor relations with the original company and claim your legitimate rights and interests. Including termination of the contract, economic compensation, etc.
3. The length of service doesn't matter. When you retire in the future, your social insurance payment and the performance of the labor contract in the file shall prevail. Attachment: Article 34 of the Labor Contract Law: If the employing unit is merged or divided, the original labor contract shall remain valid, and the employing unit that inherits its rights and obligations shall continue to perform it.