@fabceolins answer is simple and good for normal scenarios, i noticed however Excel will still contain reference to IMPORTRANGE formula which can cause access issues.
I created Google App script to copy in the following method.
If you can use Google App scripts, add the following functions:
function update_view(dup_id, TL="A1", BR="Z991") {
    // Open current Sheet
    var ss = SpreadsheetApp.getActiveSpreadsheet()
    // Supply a duplicate google doc ID. This document will be exported to excel
    var ds = SpreadsheetApp.openById(dup_id)
    // UI element for notifying in the google sheets
    var ui = SpreadsheetApp.getUi()
    //Copy each sheet one by one
    var sheets = ss.getSheets();
    for (i=0; i<sheets.length; i++) {
        src_sheet = sheets[i];
        sheet_name = src_sheet.getName();
        // If same sheet exists in the destination delete it and create an empty one
        dst_sheet = ds.getSheetByName(sheet_name);
        if (dst_sheet != null) {
            ds.deleteSheet(dst_sheet)
        }
        dst_sheet = ds.insertSheet(sheet_name);
        //set column width correctly
        for(j=1; j<=src_sheet.getLastColumn(); j++){
            dst_sheet.setColumnWidth(j, src_sheet.getColumnWidth(j))
        }
        src_range = src_sheet.getRange(TL + ":" + BR);
        dst_range = dst_sheet.getRange(TL + ":" + BR);
        //Note: DisplayValues is set as Values, formulas are removed in dup sheet
        dst_range.setValues(src_range.getDisplayValues());
        //Nice to haves for formatting
        dst_range.setFontColors(src_range.getFontColors());
        dst_range.setFontStyles(src_range.getFontStyles());
        dst_range.setBackgrounds(src_range.getBackgrounds());
        dst_range.setHorizontalAlignments(src_range.getHorizontalAlignments());
        dst_range.setVerticalAlignments(src_range.getVerticalAlignments());
        dst_range.setWraps(src_range.getWraps());
        dst_contents_range = dst_sheet.getDataRange();
        dst_contents_range.setBorder(true, true, true, true, true, true);
    }
    //Completed copy, Now open the dup document and export.
    ui.alert("Backup Complete, Please open " + dup_id + " sheet to view contents.")
}
function update_mydoc_view(){
// https://docs.google.com/spreadsheets/d/<spreadsheet_id>/
    update_view("<spreadsheet_id>")
}
To run the function, go to tools->macros->import , import the function and run update_mydoc_view().
After it is completed, export the google sheet into an excel document.