Is It Healthy To Not Forgive Your Offenders Or Keep Grudges?
Like some responses above, it really depends on pretty much two things, being whether it creates negative emotion for you, or not.
You can not forgive an offender, whilst still it being healthy, providing you're not walking around harbouring all kinds of negative emotion that keeps you symptomatic. Saying that, will forgiveness change that negative emotion? If yes, then work on forgiveness. If no, then find the solution that works for you to remove it, thus you keep your belief that you do not have to forgive, if that is your belief.
Grudges are one in the same. Nothing wrong with being pissed off at someone, and staying that way for life... but the question is always, is it affecting you negatively. If so, you have to deal with it. If not, then happy as and continue onwards.