My benchmark is usually 65% of what I bought it for, assuming it is still in perfect or near-perfect condition.
The iPad Pro in particular has bad resale because of the numerous sales stores have been giving it so soon after its launch. For those who remember, Target had a 15% off all iPad Pros, which would mean a 128GB WiFi at $807, which is pretty much what Staples is selling it right now (slightly less even...)
For maximum "insult to injury", consider Discover's 22% cash back on all in-store Apple Pay purchases (sadly expired last year). Your combination of all 3 with AppleCare+ would be (950 + 100 (AppleCare) + 100 (Pencil) + 170 (Keyboard)) = $1320 - 22% = $1030. That's less than what you're asking... you can see why it's hard to sell it at the price you quote?
Selling it all at a total of 65% or $860 would definitely draw some serious attention however. But yes, you'll be eating a huge chunk of loss.