People can have their contacts terminated whilst on the sick but the reason and wording will be significant for a tribunal case.There may be reasons of frustration of contract for example.You can change the date in writting due to circumstances,however if it is a hearing to give the outcome of their diliberations they can proceed. You say they asked for more time to look into your none attendance therefore as Wendy says you are still in procedure therefore you still have the right to natural justice,an I/T would certainly frown upon your rights not being adhered too.hope this helps