The second the first Artillery rounds go off this dude is gonna run off to souther Syria while Turkey steamrolls through northern syria. The Americans will pack their stuff and retreat to raqqa and beg Turkey to stop. Any negotiation until then is fruitless. The Americans will delay and delay then offer solutions that have no real effect on anything and behind closed doors drink to delaying the TAF. Once Turkey goes in and clears the first 10-20 km then they suddenly make serious offers, pull soldiers out, stop deliveries, high ranking pkk members suddenly "mysteriously" die off.
Because the Americans don't understand anything else then fire and blood. So for any serious negotiating to be had Turkey first needs to put its boot on the US neck and press.