From our side of things once we'd pressed aforementioned big red button there was no way to un-press it.
That is for me a real issue today in many places .
When we (ATC) go back to cancel the cavalry,(because contact has been re-established and obviously it was a frequency change problem ) some Military are replying its not your call anymore, and someone has to pay. For me this will defeat the security purpose in the long run , as controllers might be in future be reluctant to press the button ( or make that call) in time, and the real threat, if and when it comes, might be missed.
90% of radio failures are wrong frequency changes.
9,9% are "sloppiness" (turning volume down or set the wrong VHF box.)
Nothing really to justify continuing the cavalry and make people pay for these so called "mistakes" once contact has been re-established.
The one can never missed a 6 digits frequency can throw the first stone.
As Heathrow Director said, going back to previous as FAST as you can after noticing it is always the best answer.