I don't think Jeb can be arrested. Most states do not allow it of an official of his stature while on official business. You're right though, he can be impeached. But impeachment takes time. In that time, he could investigate the proper application of the law as they are applying it to Terri. He could throw his weight around as governor if he had the will to do so. He would have to decide that the life of one of his fellow citizens is more important than his political career.
It would be messy, but that is exactly what has been long set up in the state of Florida. Multiple laws have been nudged this way and that to allow a disabled woman to be starved to death, while protecting the people doing it. Do you clean up a mess, or leave it because it's just too much work?
No .. should he have an impeachment investigation/hearing .. it will have no baring on Terri and her case
Her's is a separate case and is still under court order to have the feeding tube removed