I'm afraid this is not so.
Will in a reported question beginning with 'if' is correct. Look at these, if you will:
He wants to know if he will be starting on the left side of midfield... Steve Lovell does not know if he will be in Aberdeen's starting line-up for the UEFA Cup match against Copenhagen on Thursday. He probably won't. He does not know if he will be in the north-east at the start of next season.
The above are from
The Washington Post and from a
UK site and you can see them
here and
here. There are a lot more examples from many British and American sites and I can give you more links if you like.
And I'll have to disagree that the sentence
He wants to know if you are here tomorrow is correct.
If you are going to be here tomorrow is OK.
And one last thing: A reported question (a question in reported speech) is
not a conditional clause.