San Lan became a fine example for people (who) have had bad accidents or bad luck

可以替换为that，而不能用that who

在定语从句中，关系代词有3个功能：1.引导从句；2在从句中充当一定的名词成分；3.指代主句中的先行词，即被定语从句所修饰的词。
当先行词是物时，可用关系代词which/that指代；当先行词是人时，用who/that指代。此句中，先行词为people，故用who/that都行。
也就是说在引导定语从句的3个关系代词中，只有that既可以指代人也可以指代物。但它不能引导非限定性定语从句，也不能放在介词的后面来引导从句，而which和who则无这两点限制。例子。
His father,who was 70,died yesterday.他父亲昨天去世了，享年70岁。（非限定性定语从句不能用that引导）
I can't forget the day on which we got married.我无法忘记我们结婚的那天。
（= i can't forget the day. + we got married on the day。从句中的介词on提前到了从句的句首。on位于which前面，此时不可用that替换）