If it is "common assault" it can technically carry a custodial sentence of up to 6 months, or a fine. There are some variations to the term "common assault" and what specifically constitutes the offence, but basically it is the least serious form of assault with which a person could be charged.
I very much doubt that he will only get a "a telling off", far more likely that he will have to appear in Magistrates Court to be dealt with, given the fact that you say he is already on probation for a previous domestic assault on yourself.
I take it that you made a written statement to the Police? If yes, you would in all likelihood be called to Court as a witness.
I assume your husband has to live elsewhere in the meantime?
I would think that the Probation Service would be in a position to advise re his probationary spouse visa.
Good luck.