I'd guess that it would also depend on the quality of the handstitching, too. If your stitch is closer I'd guess it'd hold up a lot more than if you have long stitches.

When I hand piece, I use a single thread and back stitch every 3 or 4 stitches. Do a double knot beginning and ending each seam. Have old quilts that were all hand done and some are well worn with the stitching intact. Some of the fabrics are fraying, but the stitching is in place.

I have some quilts I made over 25 years ago that still look pretty darned good. To this day, I still do all my piecing by hand, with a back stitch every inch or so. I do the hand piecing for 2 reasons. First, I find it very relaxing, but just as importantly, it is always portable, whereas the sewing machine is not so much. Just depends on your preference, I guess.
nanac

My Mom hand pieced and hand quilted all her quilts and some are over 50 years old and the seams are still in tac it's the fabric that gives out.

I have 2 quilts that are at least 60 years old----fabric wearing but not the hand piecing. I would have thought the thread might have deteriorated but it has not.

Hand piecing will last as long as the fabric. The solid back of the quilt takes much of the strain off of the handstitching. The quilting, whether hand or machine done adds additional strength. Don't worry about it not being strong enough to last.

If it's a straight running stitch, hand quilting may be weaker but I've had to rip out seams that I've sewed with a back-stitch every few stitches and it's actually harder to rip out than a line of machine stitching. Think about all the antique quilts, all hand-stitched that have survived for 100 years or more.

I think that hand piecing isn't as strong as machine sewing, BUT that it is strong enough for the average fabrics. IOW, it sounds like the sewing, if done decently, last longer than the fabric.

So, while I can't begin to see how hand piecing could be as strong as machine, it is strong enough.

I have done several hand stitch ones. My son has washed his so many times and the stitching has held up great.

I would not double my thread. I would make a good knot, bury it in the fabric and take small stitches. It should last a lifetime.