Thanks for clarifying, Mau.
1) I'd say pretty darned good.
2) They usually answer within 15 minutes of opening the file, but sometimes it takes them awhile to pick the file back up. If not much time has past since they countered, you likely have the same assigned negotiator, so I would say maybe not more than a week. Sometimes they don't answer at all, meaning it's $650,000 or go away, the file is "closed" unless you agree to the counter. If they do that, they may not answer at all. Remember they generally only work business hours, so weekends don't usually count as "time passed".
3) Often the written approval (which goes to the seller, not you) says they have the right to come back to the seller later for the difference between what they get from the sale and what the seller owes. The seller has to sign that. for the transaction to proceed to closing. So make sure when you "hear" that you got lienholder approval, that you also know that the seller ACCEPTED and signed that lienholder approval. The seller isn't "backing out of their deal with you" really, even though that is what happens "to" you. They are refusing to sign the lien holder approval unless they can get full forgiveness of the debt. Sometimes they can get that; sometimes they can't.
Good Luck and do make sure you are involving a real estate professional and likely an attorney as well.