Note: there is not enough information in your question to give a completely informed answer. But, yes, he can still be tried, but proof will be difficult, unless there are other witnesses or evidence. Likely, the State will ask for a continuance to give them time to find their witness, and the Judge will make a decision whether or not to grant the continuance.
not intended as legal advice
A CI may have just been needed originally to show probable cause to search. Are you certain this was at the preliminary hearing as opposed to a motion hearing? Regardless, there are some situations where they will be needed, but in most they are not.
Michael L. Doyle