If the Kings offer him 14M/Year or less, I match it.
If it's 15M a year or higher, then sorry Smart, I love you and thank you for everything, but bye bye! Then I'd really prioritize re-signing Rozier going forward and also bringing back Jabari Bird for sure this season.
Just keep in mind that any amount above $7.9M comes along with some extra costs that are pretty hefty.
1) That puts us in the luxury tax. If we do nothing else to get back below the tax by the end of the year, then that starts the repeater clock. Since we are almost certainly not going to come back down below the tax for two consecutive years in the next few seasons, we are going to get hit with the repeater penalties down the road. Thus, you need to add on an additional cost of ~20M for the simple decision to go over the tax to sign Smart.
2) Alternatively, we can avoid going over the threshold by trading away salary. That would mean finding some team with cap space (the number of teams with cap space is dwindling) to which we can trade a contract to without taking salary back. This will also cost a draft pick to get them to take on the salary. How nice of a pick would depend on the contract we expect them to take. Losing this player (for example, Morris) plus the pick would be a cost you need to add on to the decision to go over the threshold to sign Smart.
3) At least a couple of teams (PHI, MIN) are interested in Jabari Bird and are only hesitating on making an offer sheet because right now, BOS has the room under the tax threshold to match without hesitation. If Marcus walks to another team, we have no problem matching any offer and so likely no team will make an offer and we get to keep him on the QO/2-Way 75K deal. If we sign Marcus to his QO of 6M, then we'll still have plenty of room to match any minimum level contract. If, however, we use up all the space under the threshold in order to match an offer to Smart, then we would only be able to match Bird with over-the-tax dollars and another team will swoop in to make an offer sheet on Bird. Losing Bird is not the end of the world -- he's just a 2nd round draft prospect / summer league hero at this point -- but losing him, too, would be a potential cost of going over the tax to retain Smart.
I'm not saying we shouldn't do this. Danny and Brad may value Smart enough that they are willing to pay those additional costs on top of his salary. But folks should be aware that paying Smart ~8M or higher means paying a lot more on top of that.