[Grammar] Is 'all' singular or plural when used as a pronoun?

[masterthief1324]

"All" can be used as a pronoun

E.g.,
Delegates are elected thrice. All are elected once.
Children are welcomed. All are welcomed.

But there are exceptions I do not understand.
E.g.,

Everyone abandoned ship. All is lost.
All is calm.

 

[sarat_106]

"All" can be used as a pronoun

E.g.,
Delegates are elected thrice. All are elected once.
Children are welcomed. All are welcomed.

But there are exceptions I do not understand.
E.g.,

Everyone abandoned ship. All is lost.
All is calm.

I think it should be treated like demonstrative pronoun. If it refers to a singular noun it is singular and plural if refers to a plural noun. as:
Have you tested these dishes? Yes, all are good.
Have you tested all the items(=every item) in this dishes? Yes, all(every item/thing) is good

Here: Everyone(every person) abandoned ship.
All(everything) is lost.
All(everything) is calm

 

[羡鱼-Xianyu]

Everyone abandoned ship. All is lost.
All is calm.

In my opinion, 'all' here should be a collective noun, so we can treat it as a whole.