[jfman]

So we have no evidence of the costs merely the speculation that they are “significant”.

1) a figure in the small hundreds of thousands of pounds.
2) the infrastructure already exists - therefore the only relevant costs are maintenance.
3) do Ofcom do specific DTT only licences or are these the same for all broadcast platforms?
4) always enjoy the use of “may”. Presumably like 2 these mechanisms already exist.
5) not known

Until these unknown costs can be demonstrated to be higher than the revenue generated there’s no basis for the claim broadcasters will withdraw. You also ignore that the viewers forced to IP may not seamlessly transfer to watching the same content from the same provider given the plethora of new options that will be available. That’s a risk to the revenue stream that broadcasters on DTT lose prominence in millions of homes, and lose the rationale for any such prominence on IP based platforms.