A lot of times civil suits can dilute the criminal procedures, gives the defense a weapon. Such as the defense can infer the victims are testifying because "they hope to make money" or "get money" due to the civil case so its better not to muddy the waters until a conviction is secured. It keeps the motives of the victims family above reproach. (don't get me wrong I see nothing wrong with going after someone for murdering your husband in a civil matter, but it just gives the desperate defense something to use for lack of any real defense.)
On the other hand if a conviction is not secured, or he gets off scot free, a civil suit is one remedy that can ensure some price is paid for the crime. (Good example of this is OJ Simpson losing a huge civil suit to the Brown family after after the murder of Nicole and Ron after he was found not guilty in the criminal matter.)
As for the whole Scientology cult pressure forcing Fowler to do it - don't hold your breath on that one. Folwer will have to cooperate with his own defense and if he still believes or at least feels he must protect his own family from the wrath of the cult he can ensure nothing much about Scientology is brought forth at trial simply by lack of cooperation in that defense strategy. Now if he's had a change of heart or is angry at the cult, well, then there is hope for an interesting trial for sure.
(Personally my bets are on cult pressure forcing him to cop a plea, whether to his best interest or not, just to keep the flap from being broadcast in the media anymore. I would also bet his family works with the cult against his best interest and put pressure on him to go along with whatever the cult once. Still hold a tiny hope Folwer will see the light and decide "fuck this evil cult" and plan his whole defense against their greedy high pressure insanity.)