Is it possible to retrieve an interview completed and synchronised after the questionnaire is deleted from the server?

We trained our agents using a provisional version of a questionnaire which was later deleted from the server once the actual survey started.
They have been told not to use the old version of the questionnaire and they’ve been told to synchronise before the start of the actual survey.
But one of our agents did not synchronize before starting and used the old questionnaire.
So naturally, when he wanted to synchronize with his supervisor to send the completed questionnaire, the questionnaire was not received by his supervisor and disappeared from his tablet. He did not inform us before so he has not done “generate a backup” file before synchronization. Is there a way to retrieve this interview?

Negative. As per support site:

When a survey is deleted all data collected as part of that survey is irretrievably and irreversibly lost.

By deleting a questionnaire from the server you simultaneously signal to all the tablets that the interviews in that survey are no longer needed.