Usage of will after when

[Saneta]

There is the following conversation:

A: Do you know she has gone?
B: Sorry, I've got no idea.
A: Never mind. I don't suppose you know when she will be back

Shouldn't it be or can I say also: B:,,Never mind. I don't suppose you know when she is back.''?????

Shouldn't be present tense (Simple Present) after ,,when''? Why is future tense (Future Simple) after ,,when'' in the conversation?

When can I use future tenses after ,,when'' and when present tenses?

Thanks a lot for help!

[Mister Micawber]

A: Do you know where she has gone?
B: Sorry, I've got no idea.
A: Never mind. I don't suppose you know when she will be back.

Shouldn't it be or can I say also: B:,,Never mind. I don't suppose you know when she is back.''?-- No; the original is correct.

Shouldn't be present tense (Simple Present) after ,,when''?-- Not necessarily

Why is future tense (Future Simple) after ,,when'' in the conversation?-- Because she has not yet returned.

When can I use future tenses after ,,when'' and when present tenses?-- As appropriate to the time or when the main clause is conditional upon the subordinate clause:

I don't know when she will return.-- sometime in the future
I don't know when she returns.-- she has a stated, set plan to return
I don't know when she returned.-- sometime in the past
When she returns, I will speak to her-- future, main clause conditional
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Native English teacher at Mister Micawber's

[Saneta]

Thank You Mister Micawber! but please tell me if using present simple afte when in this sentence is not necessarily, so if I wrote: B:,,Never mind. I don't suppose you know when she is back.'', I wouldn't make a mistake?

[Mister Micawber]

Yes, a mistake.
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Native English teacher at Mister Micawber's