You are correct that UFT does not support Office 2016 at this time. HP does not have an official timeframe for support. This applies to the (non-automation) general support for Word and Excel.
If, however, you are concerned with the Excel.Application object, then that will still be supported in VBScript with Excel 2016. I'm not familiar with any changes to Microsoft's Excel object model in Excel 2016, so you might have to make some minor adjustments if Microsoft changed anything, but from the UFT side of things, VBScript treats the API as external to the script, so it will be compatible as long as Microsoft continues to keep the Excel API open.