I have repaired a quilt (not an antique) by taking some pieces out and resewing the seams by machine. It was treasured because her mother had made it in the 70-80? before she died. If you are not planning to go to the Antiques Roadshow but just want them nice for future display, find fabrics that will match and sew them in. I have found that many a modern calico will look good if you use it WRONG SIDE OUT. For background white or cream, sometimes a gently tea dyeing will be appropriate. Wash well before using to make sure the dye is stable.