I vote for sashing of either light blue or dk. blue if you want to keep the quilt in blues. I think the triangles will show up better. What if you used dk. blue sashing with cornerstones made of one of your print fabrics to help tie it all together. Still thinking....But you said you want a 12 1/2" block. Hmmmm....If you cut it down and add borders to make it 12 1/2" then sew them together it will be like having a seam down each "sashing" strip. (Am I making any sense?) Rather than border each block before sewing the blocks together, wouldn't it be better to just use traditional sashing strips between blocks? By the way, I'm of the opinion there is no block beyond rescuing...just plenty of creative opportunities!