It is not a valid excuse, and it depends on the state, the court, the judge, and BF's lawyer. FYI, courts don't like to deprive citizens of property or liberty, with out due process of law. Don't be surprised if the ex BF gets a second bite at the apple.
READ THIS BEFORE CALLING OR EMAILING ME: I am licensed to practice before the state and federal courts in Virginia. Addressing your issue does not create an attorney-client relationship and I AM NOT providing you legal advice. You should speak with an attorney to whom you have provided all the facts, before you take steps that may impact your legal rights. I am not obligated to answer subsequent emails or phone calls unless you have hired me. I wish you the best of luck with your situation.
I guess I am in the minority here. I say an emphatic NO. If "I forgot my court date" is the grounds he put in his pleading, he will not get another chance. This is not an issue involving children or even property. I am presuming your wife filed a civil complaint for protection from abuse against this individual. The Judge has 30 or 40 of these complaints in front of him every Friday morning in District Court. He does not get another bite at the apple.