I am another individual whose live was ruined by a chiroprator. There are several actions you can take if the statue of limitations is still not up.
First in your moms case there is overwhelming litigation that the manipulations can cause stroke. In addition, if he was manipulating C1-2 this would imply that the chiropractor would risk paralyzation. These vertebrae should not be touched.
Actions you can take:
-File a case against him in the state you live in so he would lose his license.
-You can sue (need an expert in litigation against chiropractors)
he should not have been treating stomach problems with spinal manipulations or telling people he can treat them. That is Quackery.
-Submit his name to Peer Review so people that do there research will know of his mistakes.
-Word of mouth -tell everyone you know how bad he is in the hopes that it will get around.
None of these will bring your Dad back, however, it might help someone else from this Quackery.