If a vendor is disabled, you don't see them in the suppliers' list anymore. However, it doesn't mean they are deleted. You can always activate it back, just follow the steps below:

        1. Go to Supplier Management → Manage suppliers;

        2. Click on Show filters, type supplier's name and choose Enable - "No" Filter;

        3. Select the supplier you want to enable click on Edit button in the Action column; 

        4. Move switcher in the right side of the 'Edit Supplier' row to enable the disabled supplier (a switcher should be green and show "ON")  Update.

Now a vendor is available.