You are free to open a support ticket there without providing any license key. I can help you better and faster by mail instead using this forum.
Beside of that:
Deleting the MashShare plugin folder by FTP is working anytime, no matter if there are any issues by using the WordPress deactivate function.
That’s why i resolved the topic here.
Have you already tried this?
There are more than 70.000 active MashShare users and we never had any similar support question so i can only assume that either something special in your multisite setup
One possible issue could be that you installed MashShare directly on one of your sub sites and NOT by using the network installation capability of WordPress multisite.
If thats that case it’s likely that the network deactivation is not working so you need to deactivate and remove the plugin directly from the sub site.
Again: This will work so there is no need to keep this ticket open but i will be informed if you reply here and will answer back to you of course.
Regards
René