If the trade for Harden ($41.2M) is based on Jaylen Brown ($22.7M), you almost certainly need to include Smart ($12.9M) to get the salaries to match. If the base trade is Kemba Walker ($34.3M) you can get to salary match with say Langford ($3.6M). So I look at this as Brown AND Smart or Kemba and whatever.
I don't see anyone offering years of first round picks for Harden like OKC got for Paul George. That trade was really getting BOTH George and Kawhi Leonard for the package of players and picks. Do the trade and Kawhi signs. No trade, probably no Kawhi. It is not like that with Harden. With Paul George, you also got Kawhi, with Harden, the only other thing you get is baggage.
I actually would not trade Brown and Smart (plus some picks assumed). It is not that Harden isn't necessarily worth it from a pure talent standpoint, it is just more of a lateral for the team when you consider how you are really reconstructing around Harden.
Now if it was Kemba and Langford as the base, you are keeping more of the team intact. You are still getting the baggage with Harden but you are taking the chance that he has grown up and will listen to the coach and try to fit in by accepting some level of adjustment to his game. If he does that, you are an instant title contender and maybe for a number of years. If not, you have to deal with Harden by trade or let him sign elsewhere but that will probably be the case with Kemba anyway.
As I said, I don't think anyone is going to offer a Paul George level deal for Harden. A Walker Langford start to a package will likely be in the ballpark from Houston's perspective of looking for the best deal. It probably won't be the best but maybe. Anyway, that is what I would put on the table and let the chips fall where they may.