Hi @Varun_Mittal, thanks for taking the time to share your feedback with us!
It’s currently not possible to delete a section and keep the tasks in the project. As a workaround, you can multi-select the tasks and drag and drop them in another section in your project. Then you can delete only the section.
I suggest you to add your vote to Mark Sections as Complete (in new spreadsheet List view) and Archive a Section in a Project if you wish to support these features requests! Thanks!