chances of cob.

The houses that are still inviting you back are you best chance at a house. One of your 2 pref houses should you properly rank both of them on your pref card will extend you a bid, it’s guaranteed.
Snap bids are not a given. Cob is a better chance than snaps, but also if the houses doing cob already dropped you during formal they probably won’t extend you a cob bid unless you maybe wait until next semester if grades were the issue.

If you got houses back for sisterhood round, stay in the process and continue with formal recruitment. The chances that any top houses have an opening at the end of recruitment is little to none, and if they do, it will be given to someone who they already know and want in their sisterhood. The chapters that most openly conduct COB are likely groups you don't think you'll "fit in" after meeting them for 20 minutes.