But if you don't switch them to NAV then they will stay in ALING mode, and in this mode any excessive movement/acceleration will force the Align process to restart in a way it will never finish if you take off, except some IRS models able to be aligned in flight. That means that perhaps you cannot get any info even in ATT reference mode (it will depend on the IRS model).
Finally, if you have them in ATT reference mode they are susceptible to gyroscopic precession as they are not navigating anymore. That's why you must introduce via the CDU the magnetic heading from other source.
Of course I'm just guessing as I cannot check in any manual what happens if you take off in Align
So any comments are welcome
d