You have a right to confront all witnesses against you at trial. If an officer is no longer available because he is dead, he obviously can't testify against you. Since police officers are usually the only witness in a DWI, the State will likely have a very difficult time proving you guilty.
If you don't already have an attorney you should get one. The State will likely try to get a plea bargain out of you to salvage what is left of their case. You will want someone in your corner to aggressively defend your interests.
You can call me to discuss your case further.
The state has the burden of proving you guilty beyond a reasonable doubt. To do that, a prosecutor must call witnesses, and not use "hearsay". "Hearsay" is a statement made outside of court that is offered for the truth of the matter. If the officer is dead, the prosecutor cannot use the officer's report to try to convict you. You should consult with an attorney to see how you can get your DUI case dismissed. The prosecutor may have alternative means (or so he or she may think) to try to prove the "facts" as per the deceased officer's police report. Talk with a professional about your case as soon as possible!
It depends if the officer's testimony is crucial to the prosecution's case, which I assume it is. If they are still able to prove their case without this officer's testimony (if he only played a small role in the investigation) then it might not mean much. If they can't prove their case without his testimony then you may likely receive a very favorable offer or an out right dismissal.