Ideally if LeBron left they would have had Kyrie to build around or to trade in the final year of his deal to kickstart a rebuild. I think if LeBron leaves and Thomas is still willing to re-sign, they have to sign him and then probably trade him early in the contract. They can't lose him for nothing here, especially with cap relief being kind of marginal ($12M or whatever). I don't think they can prepare but yeah if LeBron or both guys leave then I think a total teardown would be in order.