If you have multiple pets strongly bonded with each other, losing one can affect them as much as it does you. If one dies, either naturally or with veterinary assistance, always let the survivors see the body before final separation. If death occurs with veterinary assistance they should not witness the terminal event, but as soon as it's gone they should see the body. Let's go home. They'll still mourn the loss of a buddy, but if they don't get closure by seeing the body they undergo much stress wondering what's happening to their pal, where is he, who's next, and what's going to happen to them when it's their turn.
Closure is a loving gift.
I'm often asked when a new dog should be gotten after a loss. But when all your recollections are positive and make you smile, it's time to get another. And because the lost one will automatically assume huge and sterling memories, I suggest a different type. Otherwise the new one will be constantly measured against the standards the old one left, and there's no way to live up to them as we'll remember them. Give the new one a fresh start.