Closing this thread since it is now possible to delete Sections even when they contain tasks. Please be mindful of tasks multi-homed into other projects, as they will currently get deleted too! We’re looking into a way to improve this and preserve multi-homed tasks, I’ll make sure to post an update in the Forum as soon as we have a solution ready.
In the meantime, please continue adding your votes 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!