Also, one INCREDIBLY HUGE factor I didn't even mention: Dwight could very well be traded this season. It could be via Extend and Trade (not all that likely IMO), and even if it's just a straight trade, if it's to a team he likes you have to worry about them being able to extend him for more money than the Mavs can offer.
So I was only explaining how difficult it would be just by looking at the Mavs roster/financial situation and there is an entire whole other side to the risk of waiting as I pointed out above.
So to clarify: Don't sign Tyson this season, don't compete for a le, have a slim chance at signing Dwight on the chance he actually makes it to free agency.