Usually as long as the items used in the layout process, including decorations, props, furniture, etc. You can leave after the engagement party. However, if some items are specially customized or have special significance, they may need to be returned. For example, some decorations may be specially designed by the wedding company for this engagement party, in which case they may need to be returned.
Generally speaking, it is best to determine which items need to be returned according to the contract signed with the wedding company. If you have any questions about the contents of the contract, it is recommended to consult a professional legal adviser.