How likely is tfcc tear to heal in a splint for 6 weeks?

unlikely: Tfcc is comprised of a central cartilaginous component and a peripheral ligamentous component. The cartilage does not have adequate blood supply to heal itself so a cartilage tear will not respond to just splinting. A complete disruption of a ligamentous portion of the complex will not heal in just a splint. A partial tear of a ligamentous portion may respond to splinting.

Size of tfcc tear,: Location, ie in the central avascular part or the vascular periphery, instability, whther it is acute ( new) or chronic , anatomy differences all come in to play. Smaller acute tears in the periphery, not associated with instability lkely do the best.