Not sure about the black paint, maybe not original, so also most of the components seem to be from later years. Either build new just mid 90ties or replaced like the Shift- / Brake-levers from End of 90ties.
Components and Fork are not something sought after, it's rather just the frame and maybe wheelset which is defining the value.
There are still a few fans of the T24/T26, especially as the frame had an iconic design and works also for smaller persons / kids.
Just real money would be only paid for an original one with nice color and decal schemes and incl. the fork.
Due to the oversized headset, finding the right fork is even more difficult
I would guess your dads bike should be worth 150 bucks at max.