I wasn't a dog man myself, though we had a family dog when I was a youngster, I had left home when his time came so wasn't so close...But any animal we care for is sorely missed when they go, whether that is a dog or a rabbit, a cat or a mouse, it has been a part of the family for either a short time or even longer when it comes to a dog.
No dog (or other pet) should be "replaced" because nothing can replace them, but we can, when the time is right get another one to look after and care for. So when the time is right and only you know when that will be, then go and give another dog a good, kind and loving home.
It is always hard saying goodbye, tomorrow is another day, not necessarily an easy one, but maybe one to reflect on all the great years you had with Arthur.