I have never washed a completed top before and that had me nervous as well. A friend suggested running scraps from the quilt with some sample signed squares through the wash with Retayne.
I worry if I treat the ink on the squares that ran it would remove the message as well. The bleed runs completely through the words written.
I have made 9 very large memory quilts in this same manner with they same brand pen and have never had one bleed before. Hopefully, there was a bad pen in the batch. I had 10 pens out at each wedding. (so if there was a bad pen it was not at the second wedding)