Easy-out

If it has anything to do with your heater core? Maybe I don't understand your question? Take the supply line loose from heater core route it to the return line fitting on the engine block, clamp it. That should get you going till you have a chance to replace the valve. You won't have a heater, but heck, It's a hundred degrees where I am today, don't need no heater.

If I misunderstood your post, maybe you can enlighten me?

Keep an eye on the temp gage. I've done that before on different makes and models, never had any problems.