they literally have to give brunson a big contract at this point, because if he walks, the extra cap "space" means nothing since they are so far over the cap. they literally wouldnt be able to sign anyone else anyways.
nico is going to have to swing some major trades at this point. but tbh its not an impossible situation, bc the mavs were basically in the same boat in 03-04, but were able to turn lousy massive contracts into Jason Terry, Jerry Stackhouse, Erick Dampier, Keith Van Horn and Devin Harris. there are always teams out there looking for either specific talents (shooters, scoring guards), or expiring contracts. im confident he will be able to build a good enough roster in time.
the real question is whether they can find any more good value in the draft. that will be the difference between a ceiling during lukas tenure of getting 0-2 championships, or 3+