It's obvious Mika hasn't made the decision to leave yet. First of all, he says he hasn't made that decision. He's declared for the draft but has not hired an agent so he still can opt to stay. He says he believes an NBA team will draft him, he needs to say that so they see him as serious about this. But that doesn't mean he's made any decision.
If he had already decided to go regardless, he would just go ahead and hire an agent and put the agent to work for him. That would help him greatly to improve his chances of getting drafted and at a higher spot.
The question is, what will it take for him to go professional? He won't have a good feel for that for a couple of months after the workouts when he will have feedback from the NBA teams. At this point he's not a draft pick. The workouts may change that. If he becomes a first-round pick, he'll go. Second round, maybe or maybe not depending on how high and what team.
If he isn't a draft pick this year his best bet is probably to play another year at BYU and do it again next year. This year's draft is supposed to be the most stocked in years. That's not good for him getting drafted. Maybe next year would be better.
Sure, he could go the Europe route but why do that this year when he would certainly have a better shot at the NBA if he goes next year instead? This year would put him on the NBA radar and they would watch him closer next year. He has a great year next year and he could be a first-round draft pick with guaranteed contract. Win/win.
He doesn't need the money. He's got options. We'll see in a couple of months just what those options work out to be and what he decides to do.