When will my users lose Gmail access after Office 365 migration?

Hi, I'm migrating about 50 users from G Suite to Office 365 Business email. Moving accounts and inboxes also as a one batch go.
Users are already set up in Office, with their default @company.onmicrosoft.com email. Gmail currently uses their own domain as @company.co.uk.
Haven't registered the company.co.uk domain with Office 365 Business yet.
I'm wondering if, as soon as I register the domain and start migrating the users, will they lose access to their @company.co.uk gmail, as Outlook will take over the domain or will they have access on both Gmail and Outlook? I'm only worried, since it's an own domain email.

Summed up: john@company.co.uk is using gmail. I want that email to be in outlook, but afraid, that as Office acquires the company.co.uk domain, and able to use it's email addresses Gmail will lose access. Hope that makes sense.

Thank you.
Csaba TothAsked:
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Roy CoxGroup Finance ManagerCommented:
I would think that the administrator of gmail would need to manage it manually.
Csaba TothAuthor Commented:
I do have gmail admin access as well, so I can initiate the migration
Roy CoxGroup Finance ManagerCommented:
I haven't used it but check in the gmail dashboard. I have set it up for my personal gmail in the past.

This might help

Import Gmail to Outlook
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Csaba TothAuthor Commented:
Thank you.
I'm just looking for a batch migration for everyone and I can't do it for everyone one by one manually :)
The migration is not an issue with the accounts and past emails. Just worried, as soon as the domain takeover happens by Office, the users will lose connection through Gmail.
Saif ShaikhServer engineer Commented:
The best tool to migrate from gmail to o365 is migration wiz. It migrates all data.

First you may use initial sync will will sync all contents last 30 days. Then when you do cut over of mx and point all records like autodiscover, Skype you can run final sync which will sync all data.

However the target o365 users must be created with onmicrosoft.com as primary email address. Once migration is complete you can change them primary email address to your domain.
Jim RiddlesPrepress/OMS SpecialistCommented:
I would imaging that your users would have access to their G Suite account until you cancel the service, or remove the user.  Once you modify your DNS entries, no new mail should show up in their Inbox in G Suite, and I doubt that sending mail would really work, either, but they should still be able to access their account.
Jonnathan PopeCommented:
I would say as soon as your DNS host entries are modified to point to Office 365 but haven't been through the process with Gmail as yet.

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Jonnathan PopeCommented:
Sorry to be clear they won't lose access to Gmail until accounts are closed, but emails will be directed to mailbox on O365. At least that is my understanding.
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