Revisit ransomware prevention & mitigation : Sharepoint, continuous backup, etc

A related organization's critical files in 'encrypted shared folder' (not Sharepoint) just
show up with plenty of  *.zepto  

As post-mortem, they will ask for preventive & mitigation measures:

a) I suppose mapping a drive to an encrypted shared folder doesn't help at all.
    Will using Sharepoint help (assuming we don't map a drive to the Sharepoint)
    but users have to use IE/browser to upload/update/download files?
    But of course the very busy users (who almost constantly have to update
    the files, including Excel) hate to use IE/browsers to do this as it's  much
    slower than using Windows Explorer: got to check out a file & will be
    prompted many times.   Is there something as fast & like Win Explorer (for
    familiar interface)?

b) apparently the AV either did not work or not updated, will AV detect &
     stop zepto ?

c) Will IOC (indicators of Compromise) tools help with this?  Do name
    specific opensource tools

d) Exploring Acronis backup for workstations: is there a 'continuous' backup
    feature that will allow us to restore just a second or a few secs just to
    prior being attacked?