Domain migration + Azure DevOps

Due to an recent acquisition the company that I work for (Company A) needs to migrate another tenant (Company B) into ours.

Company B is running Azure AD + M365, including several other services such as Azure DevOps. 

Now to my question:

Let's assume that once we have successfully migrated all data residing in Azure AD and M365, set up the domain, migrated all mail, aliases and set up the necessary DNS-records and such....should we be expecting any problems (such as authentication, sync etc) once the companyB-users will try to log into Azure DevOps with their old login credentials?

If so, how do we prevent this from happening? Any feedback is greatly appreciated, thanks!