Very possibly both as far as the renal function. Dogs aren’t little people (as far as most species go, we’re actually the mutants in how well we handle NSAIDS, and that’s still not fantastic [think celebrex etc…]), and NSAIDS affect renal function a lot more in dogs than humans. Pred and other steroids of course have other side effects, hepatic stress being the primary one. All depending on dose of course.
That being said, when you’re looking at a deteriorating state, the emphasis has to be quality of life.
We (my wife is also a veterinarian) were dosing my in-laws’ old husky with absolutely ludicrous doses of dexamethasone in his last days (daily injections) to keep him comfortable enough to get up and be able to go out to the bathroom on his own. We warned them that if it worked for long enough, we’d definitely be causing other potentially life threatening problems, but that really wasn’t their concern. It was buying him as much comfortable time as possible, even if it caused problems. There wasn’t any long term picture, just what could be done in the short run. Not a happy place to be 
