does anyone know  
how likely some vice/cop would still be there after 6 years.

I imagine if they get to drink beer at work, they would want to stay with that gig..

also can cop refuse to testify in old case?

If properly served with a subpeona, a law officer has the same responsibilities and rights as anyone else.

The Fifth Amendment may be the only grounds to refuse to testify.

I'm not sure about testimony that might affect another case however.

(still not a lawyer)

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

thank you Von & Mr Fisher
you 2 are class acts

Dear Von, So in summary it is in LE's best intrest to  "accept the petition" as they really have zero to gain & it will cost them aggrevation to go a "hearing".
also If they do reject the petition to I get a hearing?
sorry I am so uninformed on these things. & thank you for your knowledge

First of all, I can't imagine that you could not get that record sealed just by asking to have it done.  Thats pretty common as I understand it.  Secondly, LE should have ZERO interest in keeping anything like this alive in any format after so many years.  However its really the prosecutor (City or County Attorney) who makes the call and they usually have a huge case load and if they can clear something like this, they will.  
No guarantees, but I cannot imagine that this is a problem to get done
mvr

in this world,
amazing some people go out of their way to help.
and are obviously so darn smart..
never underestimate the power of some kind thoughtful words