The guy who wrote that article is an idiot. If Durant wanted to sign with the Warriors, they have several options to create the necessary cap space to sign him outright.
Curry
Thompson
Green
Bogut
Iguodala
Livingston
Barnes (RFA)
Ezeli (RFA)
Looney
McAdoo (RFA)
The salaries of the seven players under contract, the cap holds of the three RFAs, and about two incomplete roster charges (about $550k X 2) would put the Warriors about $3 million over the projected cap. That means they would have to shed about $28 mil to create cap space for Durant, but that would be easier than that writer realizes, as the Warriors will have a lot of tradeable contracts.
Bogut (age 31 in summer 2016): one year, $12.7 mil
Iguodala (32): one year, $11.1 mil
Livingston (30): one year, $5.8 mil (only $3 mil guaranteed)
Bogut made the All-NBA defensive second team this season. Iguodala was Finals MVP. Livingston has value on that modest of a contract. That's nearly $30 mil worth of contracts for which the Warriors should be able to find takers, especially given the number of teams that will have cap space next summer. That's enough to create max space for Durant, and that's without having to renounce their rights to Ezeli (Bogut's successor, if they need to move Bogut to create cap space) and Barnes.
Trade Bogut, Iguodala, and Livingston without taking salary back, sign Durant, use the room MLE to sign a cheap vet, and then go over the cap to re-sign Barnes and Ezeli (both will earn more than their cap holds, so it makes sense to use cap space to sign other guys, then go over the cap to re-sign Barnes and Ezeli):
C: Ezeli
PF: Green
SF: Durant
SG: Thompson
PG: Curry
Bench: Barnes
Or you could start the most unstoppable offense in NBA history...
C: Green
PF: Barnes
SF: Durant
SG: Thompson
PG: Curry
...with Ezeli coming off the bench or starting when matchups dictate it.
The rest of the bench would be sparse...
Bench: Looney
Bench: McAdoo (?)
Bench: Player signed with Room MLE ($2.9)
Bench: Player signed with Bi-Annual Exception ($2.2 mil)
Bench: Minimum player
Bench: Minimum player
...but that team would be able to snag some half-decent ring-chasing vets with the room MLE, BAE, and minimum contracts.
And since they changed the CBA in 2011 so that players can't earn more via sign-and-trade than by outright signing with another team, it wouldn't benefit Durant to do so.
One potential monkey wrench in all of this is a Harrison Barnes extension. If he and the Warriors agree to an extension, then that would eat up millions more in summer 2016 cap room (unless Barnes signs an extension for less than 4 years, $43 mil, but that's highly unlikely, given the current market). However, even if the Warriors extended Barnes, they could easily trade him next summer if his new salary were large enough to stand in the way of a Durant signing. In that case, they wouldn't have to dump Iguodala's expiring.
If the Warriors want Durant, and Durant wants the Warriors, they can make it happen without trading Thompson.
