I guess there's a slight danger of parasites or disease left by the departed wasp. Maybe steaming them would reduce the chance of that.
Hm perhaps... The funny thing is, I have never seen a gall with an exit hole.... All galls I've seen people collecting as DIY ornaments, and all I have collected were whole. I only collected those that have fallen off to the ground.
It was believed until a couple decades ago that the gall is oak defence mechanism against the wasp. A callus, if you will.
We have a special semi-evergreen type of Dalmatian oak that is quite different from your regular oak. It is shrub-like and rarely grows taller than as high as you can reach with your arm. Even the leaves don't look oak like: https://hr.wikipedia...ki/Hrast_crnikaIt can grow tall but that takes a hundred years and fires in this arid region don't allow for that much.
So it's quite possible these galls are different than those from regular oaks. Possibly produce a lot of "failed" ones. I would bet it is due to harsh dissecting sun. If your mom did not have the savvy to induce the gall in the shade, under thick leaves, you're toast little wasp.
I believe these to be well dissected and sterilised by the heat/UV, at least around here.