No you have to keep spraying, year after year. Or replace with scab resistant varieties. If you are in the US try the web site or local branch office of your state Cooperative Extension Service for more information. Including what particular chemicals and timing of sprays are recommended.

Sorry, no, the tree will not be cured permanently. Scab is a fungal condition and will regenerate each spring when climate conditions are suitable for its growth. Some trees are very susceptible and others may be very resistant.

Fungal spores can overwinter in any litter on the ground (fallen leaves, etc. that have not been cleaned up and disposed of) as well as on the stems and branches. Proper sanitation can certainly reduce the occurrence or the seriousness of an infection but will never cure it completely. You will have to spray every spring to be clear of the disease.....and even that may not be 100% effective.

Generally, scab is considered to be more of an aesthetic problem - the fruit under the scabbed skin is typically unblemished and perfectly edible - but a severe infestation will cause premature leaf drop and that can weaken the tree over time.

There are lots of extension service fact sheets online that explain the life cycle of the disease in some detail and how best to approach its control. And lists of scab resistant apple and pear varieties. You might want to spend some time Googling and reading up :-))