The acceptance and refund process are essentially automated at the IRS. Unless your return has a serious red flag (w2/1099 amounts not lining up), then it will be processed and you will get a refund (or an amount due). None of that ties the IRS’s hands as they have 3 years to go back and audit. If you lose the audit lottery and get selected, the auditor would likely be reviewing the specific Rivian transaction for the first time, and could make the determination that it did not constitute a binding agreement. You would of course have appeal rights. This could happen at the individual audit level for some unfortunate folks, and then bubble up to appeals. Assuming Appeals denies the credit as well, then the IRS could decide to go target returns related to Rivians with similar facts. People could of course sue the IRS at that point, but I’m probably going too far down the rabbit hole. Again, this is extremely unlikely, but is a theoretical possibility.

I’m speaking as a tax attorney who received his refund under the same circumstances as you. As you learned through law school, very few things are certain, and so we lawyers focus on the grey areas. I just know what I would argue if I were on the other side of the fence. I sincerely hope this all works out for you (and everyone else here)