There is one accepted way to control another application, and that is through OLE. But there is also an accepted, gentlemanly protocol which determines how you should handle your connection vis a vis any others...

If you need to use Excel, you must do it in a way that has no impact on any other application's use of Excel, nor anything that the user may be doing directly from the user interface. The prescribed way to do this is to address all of your attention and your commands to OLE document objects (in this case a "spreadsheet" or "workbook"), and not to the servers which support them.

OLE knows what applications need to be started, and whether they need to be started or not. It also knows when those applications should be closed down. You should not tell Excel to terminate because, although it will obey you, doing so pulls the rug out of whatever the user might be doing! Leave that to the OLE subsystem only.