So why not deal with the Clippers and try to get a haul from them? If the Clippers didn't bite, talk to the Lakers and play them off against each other to outbid the other for Kawhi. Scare them into thinking they're going to lose out to the other LA team if you don't make a move now. They both thought they could just wait until the off-season and sign him outright, but if you were willing to deal him to LA, then you could have closed that option down for one of those teams. I don't know if the Spurs did that or tried doing that?
IMO, they should have went in looking to trade him to the Clippers, but if the Clippers weren't offering enough, see what the Lakers had to offer, but don't trade with the Lakers unless they gave an insane offer. I still think the Spurs messed up. I didn't even want to trade him at all if the package wasn't good enough. I would have waited until the trade deadline or even just let him walk at the end of the season if all the offers were garbage.
If the Clippers offered both last year's draft picks and Tobias Harris, would you have taken that over Derozan and Poetl? I would have if I had the choice between those two options.