As far as I know none of the corrections are applied by the system in Attitude since it has no idea where it is on the earth's surface, so it is using the earth's gravity to produce an attitude and requires a heading input at frequent intervals. I have never used it, so I do not know what would happen if you failed to input heading.
This is a guess.
I think you would still have a usable attitude display, but bear in mind the heading requires a variation input which is constantly changing with position (which it does not know) and the derivation of heading would not be corrected for earth's rotation or aircraft motion and thus would become unreliable fairly quickly.
Edited to add an afterthought
