had he not been kind,he wouldn`t have succeeded.这是一句虚拟语气的句子,换种说法就是If he had not been kind,he wouldn`t have succeeded.
含有助动词should、could、had、were这样的词,可以与主语倒装同时省略连词if.
only if 是主句倒装,从句不倒装.从句也就是紧接在only if 后面的句子.给个例句：Only if you eat the correct foods will you be able to keep fit and stay healthy.