There is a discussion on this topic FE NXT General Discussion - under "Is there a way to update Vendor Statuses for many vendors at once?"

Solution- You can update vendor's through imports. You'd just need to enter in a vendor import where the status is now Inactive , and run the import. Main thing is just building the import file, If you have a query that captures the vendors, you could export that and then just update the status field and import that. You would use the import option, but with a status of Update. This would allow you to update an existing vendor, such as changing their status from active to inactive.

I updated several hundred vendor this via the import recently and it was quite easy.