The current context menu lets you hide a row or column, but then you cannot show it again, so the user can lose data. At present there is no context menu option to unhide it and there is no element indicating the column/row was there in the first place. This should behave like in Excel.

Such a feature must be implemented first in the underlying Kendo Spreadsheet widget, and to this end I encourage you to cast your votes for its implementation here: http://kendoui-feedback.telerik.com/forums/127393-kendo-ui-feedback/suggestions/19240072-context-menu-option-to-unhide-row-column