Would the Mafuba even work? Because..

[UltimateHammerBro]

I don't think it'll work. Sealing them away would feel like the easy way out.
That said, I can't think of any reason why it wouldn't work. I don't think it's exclusive for demons (nor has it ever been used on a real demon). Heck, it can't even be limited to evil people: Goku used it on Turtle

[Lionel]

Teleportation doesn't allow for the sealed victim to escape. If it did then Kami would have appeared outside of the sealing device via Kai-Kai which he's displayed before. Also, the Mafuba should logically kill the user as it is projecting all of their genki during the sealing ritual. Relative strength should be inconsequential given the magical nature of the sealing. In that respect, it's similar to Babidi's spell used for entrapping Buu.

[floofychan333]

some other dimension

They don't get sealed in a different dimension, they get sealed in a container like a denshi jar or bottle. And they apparently can't take action when in that state since they can't simply break out. Are they even fully conscious in there?

They're conscious, and I guess they would survive on moisture? I'm sure any human would die in the Electric Rice Cooker but King Piccolo only needed water (moisture) and had a really long lifespan so he could have survived it.

[Mazingerdestro]

The only reason I could see Goku sealing Black, is so they can later use him in the tournament. It would be so ironic to see Black been forced to participate in the final tournament and the only reason would be Beerus threatening him.
Maybe keep him sealed for the next 5-whatever arcs, till the final tournament starts and everyone is at least at God level so out of nowhere Beerus explains that he has a "secret fighter". Everyone is going to think that it's monaka and then Black appears