If there are no witnesses the DA will have a harder time proving it's case but could do so through other kinds of evidence. I hope neither you nor your husband are thinking of dissuading witnesses or worse as that would be a new and separate crime.
There may be ways for the DA to proceed without the witnesses, but your husband's attorney should be ready to challenge any hearsay testimony, etc. If the witnesses testified at the preliminary hearing and are now unavailable (again, your husband's attorney should fight this aspect), then the DA may be able to introduce their testimony from the preliminary hearing.
And here's the other thing to consider... on a felony, the DA can dismiss and re-file the charges on a felony and basically start over.
If they don't show up on their own, it can only benefit your husband. If they don't show up because of something you or your husband do to try to get them to not show, that's another story. That gets nothing but worse for him.
There is not enough information to give you a full answer, but based upon what you've written, two eye witnesses are certainly enough evidence to prove a case against anyone. If they don't show up for trial, then the DA wouldn't have much of a case left by what you say. However, before you rely upon them not showing up, be very careful. I've heard that from many Defendants over the last 35 years, but its only happened once and then, yes, the case was dramatically reduced, not dismissed.