This breaks my heart.
First of all, speak with the Broker. There is no "If [the Realtor] aren't willing to do it then...." We are all agents for, and acting on behalf of our Broker. As an Agent, we do not have the authority to release you. The Broker does, and should. You should have the freedom to list with anyone you want to.
That 60-or-so-days that was mentioned here, where you would still have to pay the commission is designed to protect the Broker, when the homeowner pulls the house off the market. For example, your Realtor shows the house, and has an interested buyer. You want to work out a deal with the buyer, and avoid the commission, so you pull the house off the market. Depending on your contract, you might still have to pay the commission. This generally does not apply when moving from one Realtor to another. Why? Because, we can still bring a buyer, and receive a commission (although, not as much).
If the buyer does not have their financing secured, that is a contingency on the contract. Contingent, or dependant on, means there are still loopholes, and the Realtor should caution you on doing anything (like the abstract), until those contingencies are removed. Sure, the contract could fall apart at the closing table, but without contingencies, it is less likely. The standard timeframe for removing contingencies, inspections, etc, is 10 days, although it can be whatever both parties agreed to.
Why was this Realtor not used in your new home purchase? It is easier for the Realtor to help you with both. When something gets off track with one, she can immediately adjust the other one, so it is as seemless as possible for you. Find a Realtor who you really like, and seems to care about your needs. Found a Realtor you really click with, but he doesn't seem to have the knowledge of the last one you spoke with? Talk to his Broker. Be honest. Tell him that you want to work with him, and why, but you want him to stay in consultation with his Broker, who has the bulk of the experience. Be polite, but don't worry about hurting his feelings. We know why people can be skittish about Realtors, and completely understand.
Just like in any other industry, there are bad ones out there....but there are good ones too. I've never understood why people just call the listing agent on the sign, on every property they are interested in. It is well worth it to find a Realtor who is right for you, and staying with them for all your real estate needs. That may sound like a marketing line, but it will minimize stories like this.
Hopefully, you can salvage the contract on the home you really want. There is a chance to get the first-time homebuyer's tax credit up front now (in the form of a short term loan). Maybe, the buyers could tap into that. Good luck!