Can you post a photo?
I'm not quite understanding the result. Are you concerned because the yellow batik is not as yellow as it used to be? Or was the yellowing the result of the pet accident, and you want to get rid of all of it?
How did the seams come out? Did you get any fraying?
Synthrapol is supposed to be used in hot water to be effective, but I have found it still works to a lesser extent in non-hot water. Depending on the problem, it can take several washes with Synthrapol to get a stain out completely.
Drying usually does not permanently set dyes or stains, so I wouldn't be overly concerned about the fact you ran the top through the dryer. I am more concerned about how much agitation the quilt top can take before you start getting frayed seams.
If your concern is because the yellow batik is no longer as yellow as it is supposed to be, that means dye has been released from the fabric. The only way to restore color to the fabric would be to use fabric paints or some other type of color restoration on it.
If your concern is that the yellow stain did not come out completely, then I would consider finishing the quilt as is, then treating it with Retro Clean (
http://www.retroclean.com ). Actually, if you think the quilt top can handle it, you could try soaking it in Retro Clean now.