In real life coincidences happen all the time.
Coincidence isn’t allowed in fiction–at least not to solve a plot point.
Readers feel cheated. You took them for 200+ page ride and then you resolved things with an act of God.
Robert McKee, the grumpy screenwriter guy, says that you can’t use coincidence beyond the first half of a book. That makes sense. You can use a coincidence to start off a story but you can’t resolve the plot in that way.
So if you got to the point of your manuscript and you’ve backed yourself into a corner don’t roll out the tornado, the unforeseen inheritance or the mystery good Samaritan.
Suck it up and make your characters go to work.