Once in a lifetime trip, or visit elderly sick parent?

My mother in-law is having a dilemma and I would like some outside perspective. She is 70f and has a chance to go with a church group with her best friend to Europe for 2 weeks in July. However she was recently informed about her father 95m who's health is declining. He is stable now but had had recent health issues. He also has cancer and is being treated for it. Her siblings who live near him are caring for him and tell my mother in law to go on her trip. She also spent the last 4 months living with him to spend time together since he lives out of the country.

Her dilemma is wheather she would feel guilty if she goes on her trip and something happens when she's is on the other side of the world. Should she still go on her trip feeling uncertain of what could happen, or should she cancel her trip and visit him instead.