Could be either yes or no. Is the old domain being dropped? If so you need to speak to whoever is in charge of the migration. Ideally you want to go from this
With a subdomain
Then you can get to your old data via archive.newdomain.com/oldadminpanel
This is the most cost effective solution for most. Also that way you are asking that the old site is maintained in terms of data and files. Otherwise you might lose something.
If the old domain isn't being dropped access will be maintained for as long as you continue to pay for hosting for old domain.