Phil Richards wrote in
T:

Although there is no expiry date, no doubt TfL/LOndon Buses have got
hidden somewhere in their Conditions of Carriage that they have the
right to withdraw the product when they want.

What notice would they give, and would they refund the cost of any unused
tickets?
I got caught on a similar thing when Mercury (remember them) withdrew their
payphones. I had unused credit on a calling card.