It is advisable to set the disable access by setting the account status as "Partial" which will not restrict mail flow but deny access. 

The O365 domain verification failed when configuring the co-existence setup with SkyConnect. What do I do?

If the domain verification fails, then it is possible that the domain has been verified for another Microsoft Online Services account. To proceed, make sure that the domain is moved to the correct account.

For details refer to the following topic:

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