The new signal system has the ability to allow non-ATC-equipped trains to run through it. Much like the original wayside signalling system, it is configured into blocks that are delineated by the wayside signals. But as each block is much, much larger than the those of the old wayside system, that also means that operating non-equipped equipment greatly reduces the throughput and capacity of the system.
In an emergency such as this, that isn't really that big an issue. But it certainly precludes the ability to do so in regular service, as the trains would have to be so widely spaced apart as to be a problem.
Dan