Oh David, I am so sorry this happened. Looks like you are dealing with two things: a really bad tear and very old fabric. I have a couple of quilts that didn't receive an injury but just are falling apart with age and wear that are family heirlooms. I have them put up...don't know anything else to do. Again, so sorry.

the archival way to repair and restore is this:

lay it out as flat as possible. wherever the batting missing, pat in thin layers to bring it up to the level of the remaining batting.
we're still keeping it flat. layer tulle (netting) over the holes or the weak places that are apt to tear in the near future. think of this as the framework. the rest of the quilt will hang onto this. with teeny stitches, do a running stitch all around the torn places, not pulling, but butting the edges up against each other as best you can. we're still working on the first side, but it doesn't matter if the stitches go through to the other side. don't make big stitches. they'll get caught again. after the edges have been sewn, start stitching inside the weak places or torn palaces. you'll end up with a rewoven area, loosely filled with small stitches. flip it over and repeat. drink some wine.

trim away any excess tulle there may be along the outside edges and patch the torn areas with soft fabric as close in color as possible to the original.
as long as it's soft it doesn't have to be old. faded is good, but old will be weak. the tulle on the inside will allow the quilt to hold onto something without putting all it's weight on the weak, old fabric around the tear. the patches will cover the tear and the tulle. make your stitches as small as you can.

remember, this is a loved quilt. it's done it's job. it won't last forever. eventually it will be beyond repair. start loving a new quilt.

That is what to do. Take it apart and re-make that section of the quilt. Don't panic! The quilt will tell you what new/old pieces you will need.

David I think I may offer some help to you. I have done repairs on quilts. I just finished with one. First there are 2 options to consider. First can you see enough of the other pieces to cut some material to sew over the torn pieces? It need not be new so as to keep in with the other blocks. Maybe some retro of 4os style material For white in the older quilt they used unbleached muslin. Get a good grade of this if you can. Pin the prepared pieces over where the tear is I like to prepare the top first. After you add the prints and color to that part torn Hand sew this in plac. Turn the quilt over. You can cut smaller pieces of low loft batting and place it where the old batting was. Just in the torn area. Now I could not see what kind of backing was originaly there. If you have too you can replace the whole backing. After it pleases you ,pin in place Now check the edges. If they are okay Then begins you journey of hand quilting. Maybe you can get some volunteers near you to help. Idone one that had been in a fire and did not have to replace all of the back. I then hand quilted the repaired parts in the same design the quilter had used. When these people came to pick it up He cried as it was made by his GM. I asked a small fee asI felt it was more important he have his quilt. He sent his daughter back with more money and he gave me 2 1/2 times what I asked.
Can I send #2 idea in another post?

Debbie as we know our quilt family has probably got scraps that may match any he has to replace . I would be glad to go through mine to ceck and see. The pattern looks like it may of been an Inproved 9 Patch. Where the corners of the 9 patch come to a sort of point. There seems to be turquoise and some white like shirting. An old pair of pillow case from Goodwill could furnish some maybe the right weight and softness. We can all use this as an oppertunity to help a fellow quilter.

Sorry, Im a day behind reading the posts so you may be feeling better today, I hope. I too am disabled with a pain disease and clinical depression. Do not let this get you down. We have enough that gets us down. Your sweet grandmother would just tell you not to worry about it. I hope that you have found the answers you needed. You got alot of good responses. the quilt on my bed was my first ever quilt and our beagle slept with us on it for over 9 yrs and completely wore out 2 of the squares. I found some scraps and remade them by putting in a new square of batting and then whip stitching the blocks back and on the back I did the same with a new block. Then I requilted on top of them. Noone can tell. I pray that God will send his angels to comfort you and your quilt will be just fine.

When he gets it to me, if he doesn't decide to take it on himself with all the wonderful advice on here, I will look at it and then see. I have old pillowcases too and older scraps. Will have to see it up close and personal to see. Thanks♥♥

As you pin the pieces back together as well as possible, maybe try using some 505 Basting Spray to hold them since that may be less stressful on the old fabrics than pins...?
or even some fusible webbing to hold them until you can requilt them to the reinforcing fabrics behind them that were suggested here.
Bless you for loving that wonderful old work of art so much!

Please post photos of your restoration, too, because we all care and appreciate your frame of mind over the damage.

I would unpick the square and try to find fabric similar colors. Make the block(Sandwiched) and hand stitch it into place. Do the back first then whip stitch tiny stitches on the front. Please let us know how it goes.

Oh David, I just got back from a computerless vacation. Your story hurts my heart. But...you did get some great suggestions from out lovely quilting boarders...please keep us posted on which method you use and the outcome. It will be an inspiration to all us newbies...