I suspect the reason the usual posters have not answered this question yet is because it is a tough one. Let me give it a try. Lawsuits against drug companies are very very tough to win. Drug companies are very rich and don't like to get sued, so they defend vigorously. The laws are largely stacked in their favor. Until recently, cases involving inadequate warnings on medicines were routinely thrown out of court on the basis that the FDA had the final authority on how to label drugs. That changed a year or so ago, and now in theory it is possible to bring such a case. As a practical matter, few lawyers will touch a case for an individual plaintiff against a drug company. Most such cases are brought for large numbers of plaintiffs. It would be worth your while to find out if any lawyers are handling mass cases involving lipitor. If there are any a google search would probably turn them up. You should also consult with a medical malpractice lawyer in your area and investigate the possibility that the doctors who prescribed the lipitor and watched your father get sick as a result of the drug acted within standard care.
As the prior answer said so well, just because it seems like you "have a case," doesn't mean that in the real world you can win it. It is expensive and daunting to win against a rich and relentless drug company. You would need to hire several experts to have any hope to prove the drug caused the problems, and that a label might have prevented this. Also, you will likely have to do some serious digging into what the manufacturers knew and when they knew it.
In short, it's expensive.
That's litigation of this type.
I think you owe it to you own piece of mind and your father to consult a competent lawyer who practices in this area. You will need to arrive at an arrangement as to what costs the lawyer will absorb and such.
I wish you luck.
Sign up to receive a 3-part series of useful information and advice about personal injury law.