On-premises AD migration in O365 tenant

Hi all,

Current environment:

AD - AD connect- Exchange hybrid in O365.

All mailboxes have been migrated to O365 and everything is working as expected.

The old AD will now be decommission and moved to a new AD. How can this be achieved?

If we use ADMT to migrate those accounts from old AD to New AD, what happens to azure ad and AD connect?

thanks.