Planning ends when project finishes or it continues till the complete cycle of the project and post project cycle as well?

Planning doesn't end when project finishes.
Of course project (for that specific project) planning ends as soon as objective of that project is achieved.
From an organisation point of view, all information (key findings, cost information etc) related to that project should be properly stored and managed by an organisation.
So that that information serves as one of the input for planning for next (future) project.

Ultimate goal of Planning is to achieve the prediction as per plan,If you are manufacturer the plan for a product and it get consumed as per plan that is the achievement so planning ends when it fulfill the task whereas some cases it needs to be continued to fulfill another ancillary activities as well.