第一个问题：

Were it necesary(=If it were necessary), I might go without delay.

Had Jack recognized his teacher(=If Jack had recognized his teacher), he would have run.

在含有if 条件句的虚拟语气句中，如果有“(1) had + 完成时 (2) should +原形 (3)were/ were to + 原形” 三种情况时，可以把 had, should, were 提到主语之前，然后省略if，构成语法倒装。这类倒装是为了表达简练和多样化。

例如：

Had she studied harder, she would have passed the exam. 如果（以前）她学习更加刻苦的话，那么她就会通过考试的。

Should all the water on the earth disappear one day, what would happen? 假若将来有一天水在地球上全部消失，那会怎样呢？

Were it to rain tomorrow, we would put off the basketball match. 明天下雨的话，我们将推迟篮球赛。

第二个问题：

Should he come(=If he should come), tell him to come to my office.

这一句，红色部分表示“推测或可能性”，不是“虚拟语气”条件句。

should：MODAL (用在条件从句中表示事件发生的可能性)将要，假定要：

You use should in conditional clauses when you are talking about things that might happen.

If you should be fired, your health and pension benefits will not be automatically cut off.

如果你被解雇，你的医疗和养老保险金不会自动中断。

Should you buy a home from Lovell, the company promises to buy it back at the same price after three years.

如果你从洛弗尔公司买房子，该公司承诺3年后以同样的价格再购回。