I think Willie is a goner. I think he starts the season with us, hopefully plays very well for some teams to give us something meaningful, and is gone.
I actually like Willie, and say this without any malice. However, we have 6 bigs on the roster, including 4 young guys, none of whom can shoot from outside. In the modern NBA, that's like having 4 bigs too many. Willie is the one likely to get the highest value in the short term. Plus, we have to decide on his contract soon.
The only way I see him continuing next year with us is if Giles hype is proven to be false, and/or we trade Bagley for someone like Kawhi Leonard. Very unlikely, given that he has clearly expressed his interest in playing in LA. However, if he does agree to extend with us, we can provide the Spurs with several expiring contracts, additional cap space for next year (by absorbing Pau's salary in our cap space, and some exciting young talent, including this year's #2. Short of landing a star, this is not a bad haul for them, and will allow them to rebuild from scratch.