I have a question about tense:

I am wondering which tense should be used after "Gone are the days when..."-past tense, present tense, or either?

Past tense makes more sence to me, but I encountered a sentence recently saying that "Gone are the days when we can lead an isolated life...". My friend says it is an attributive clause stating the fact, so present tense is used here, showing that the writer doesn't want to emphasize the past. Is it correct?

Some also say that if you used present perfect before, then it is better to choose simple present tense than simple past tense in order to keep consistency. Are there rules like that in English?

Thanks a lot for your help!