I have to agree with Chico2 on this. We are all animal loving people here and would never ever suggest anything of the sorts unless there was no other option.
We have supported one another here on this forum when we had difficult decisions to make. It has not been easy and it is very painful, but as animal loving people consisting of rescues, shelter workers, volunteers, animal welfare activists, volunteers and regular animal loving people, we truly stand by quality of life.
Best to you all. I wish you strength.
Please note: Labs have a very high pain threshold, you cannot tell if they are hurting but there are signs such as significant behaviour problems that start to develop that are completely out of the ordinary.