I ran into this in a novel
"... I hope you will get over it, and live to see many young men of four thousand a year come into the neighbourhood."
"It will be no use to us if twenty such should come, since you will not visit them."
"Depend upon it, my dear, that when there are twenty I will visit them all."
Does "if twenty such should come" equal "I know the possibility of coming 20 such is very small, but if they came"?
I have searched on it and found out when we have "should" in our if-clause it denotes the small chance and unlikeliness. Then may I paraphrase "Should Jack call, tell him I'm not going to talk with him ever again" as "I know it is unlikely that Jack make a call, but if he made it, tell him I don't want to talk to him ever again"?