[sc11]

Signalling still works, so you can let the trains continue to a safe place like a station and then not let them leave until the radio issue is resolved

[PLenz]

That depends, cab signaling for example needs radio to work

[LargoLasskhyfv]

Not necessarily, at least for some time:

https://de.wikipedia.org/wiki/Linienförmige_Zugbeeinflussung