could this possibly be a prelude to a S&T for JH for Sheed's deal where we also take someone the Wiz want to dump in addition to Howard? I believe there's a delay in doing an S&T with a just-signed player if they're being traded with somebody but would that timeframe have elapsed before the season starts?
No, a sign and trade has to be immediate. Once the contract is signed, if he is not traded right away, he cannot be traded until December 15th.
My guess is the C's could not work out a reasonable sign and trade because they couldn't decide on option years. I believe a player needs to be signed to a 3 year deal to be sign and traded, and Howard probably did not want to give the C's team options for those last two years, in case he completely recovers, and is worth more, and the C's didn't want to give him player options for those years, in case he does not recover fully from the ACL tear.