Delete Group but not Team

Cian is right, you cannot have a stand alone Team. The reason why the group got deleted and it took awhile cause of just back end processes. When group is deleted it doesn't really get deleted goes into recycle bin etc. so the Team still references the object, then eventually cleanup job kills the Team too. Most of Teams has azure tie ins and mostly ties into Mailboxes with Exchange online and new Skype for Business stack.

You best bet, is just pretend the group isn't there and hide the addresses from the address list. But a group is def. requirement of a Team. You also get a SharePoint site with the group as well. 

Here is a very good info-graphic going over what gets created with each type of product you start from etc.