They should max out Klay. Even if it's an ACL tear (worst case scenario), surely he can come back the as the same guy. So does Kevin Durant. Just think of it as the first year of his contract as compensation for the image hit, the discounts, the injury, and the two rings he gave Golden State.
In the meantime, they should go and sign Reggie Bullock and Jeff Green.
Bullock is no Klay Thompson by any means, but his shooting is above average, and he is about the same size. As for Jeff Green, motor is and has always been an issue, but he still can go, on both ends.
As a stop gap, and for the cheap, they are decent pieces.