The rules on suing can be complicated. Though there are some rare exceptions, generally, the rule for those who have had a PEB prior to separation or retirement is that you have to sue within 6 years of leaving the military. The time spent for administrative appeals do not halt the six year clock from running. Given that, it seems that you will be unlikely to have many options left.
As for whether it is worth fighting, I don't think the analysis is as simple as faery_glamour suggests. In some cases, it is true that there is no additional gain to be made by getting a higher rating in terms of money. However, depending on your rank, length of service- which will determine the amount of your retired base pay, you can end up with (sometimes) substantially more money. In addition, there are situations where you can "double dip" from military and VA pay, for example if your conditions are combat related or if you have 20 years or more of service. Finally, do not underestimate the value of the TriCare health care benefit, which would be available to the member and eligible dependents.
To sum up, for some people there is no advantage to a higher rating (or even a retirement finding). But for most folks, it is better to be retired, if for no other reason than having the health care benefits.