English Question: Difference between these sentences.

I am quite confused about these sentences.
I know the word “Gone” is past tennse of “Go” and it can take object and can’t.

1. The pain has gone.
Here the object is “The pain”.. but what if this sentence is made as
1. The pain is gone.

Does it have the same meaning?

2. Those days are gone.

Similarlly,

2. Those days have gone.

Also, Are these sentences correct? Do these have same meaning?

He is not here, he has gone out.

He is not here, he is gone out.

The verb gone used here is intansitive, I think.

Please help me out!

Best answers are appreciated.

Thanks!