Vice tends to be a temporary rotation for officers in most departments for two reasons.  First, their face gets known by the people they are trying to work and they become less effective.  Secondly, all the involvement with booze/broads/whatever is not conducive to the officer's personal stability (they ARE human, you know) and can destroy the officer's career/marriage/life if he gets too deep into things.  
The odds of the same officer still working Vice after six years is slim to none unless he has risen to supervisory status.
Regarding court appearances; yes, as usual, Mr Fisher is correct, in theory, the cops are as obliged as you or I to respond to a subpoena. However, there is usually little to no consequence if an officer fails to show up for a misdemeanor proceeding.  
Step one in your case would be to find out if the officer is still even employed by the department. Call their non-emergency number and just ASK if he is still an officer and for his work number.  He was not a 'rookie' when you encountered him most likely and its six years later.  There is a real possibility he moved on to something else (another department, the Feds, high paying contractor work in Iraq, etc) or otherwise was terminated.  If he is no longer a sworn officer with that department, the chances of him showing for your trial are very low.
mvr