Now or later

Day before yesterday my mother-in-law's mother-in-law fell down and broke her hip. My grand mother-in-law (don't know if that's the right word for the relation) is almost 90 years old. She had to undergo surgery. It was a very risky surgery considering that anesthesia can be fatal at this age in some cases.
                                                   As a result my in-laws who were supposed to be visiting us for a month had to cut short their vacation and rush back home. My grand mother-in-law survived the surgery. But she will have to be on bed rest for about 3 months which sure isn't a pleasant thing for any age!
                                          This episode made me think about how short lived our plans are. We can go on making as many as we would like but life, destiny, time, God (or any other name you would like to give it) can change them anytime. Like in this case there were things that we had planned to do in the later half of the vacation - go out for a short trip, celebrate Diwali together - which we wouldn't be able to do now.
So does this mean we shouldn't make plans?
Or should we go ahead but be flexible when life throws a spanner into our plans?
Whatever the choice - this and many such incidents make my belief stronger that there is something called destiny!