Oh my god, you must have told avast to delete them as avast doesn't delete automatically.
avast scans and alerts you to infection and if you have the home version gives options and you make the choice, move to chest, move and rename, delete, ignore and repair (if available), etc. and you must have chosen delete.
The avast pro version can be set up to take automated action on detection and you can choose on an option like Repair, if not possible, move to chest, move rename, etc. but, again there is no autonomous deletion of infected files, the user must either interact and make a choice or have set it up to take action automatically.
So there should be no problem in keeping avast running when you are working with xls files or any other file unless they happen to be infected in which case the 'first do no harm' don't delete.
Deletion isn't really a good first option (you have none left), send virus to the chest and investigate. If you really have deleted them and not sent them to the chest you may be luck and use a file recovery tool undelete or something like that or you will have to use your back-up to restore them (you do back-up your data files.
Are you really sure you have the same problem as 1) MW97 is a microsoft word related micro detection and 2) the VPS of 9th Dec more than 2 days ago. So you must ensure that you have the latest updates.
