Hi Mohammed,
According to the error message received, this issue can be caused if the certificate of the ADFS server (for another domain) is expiring. You will need to renew the token-signing certificate referring to resolution 2 in the KB article: http://support.microsoft.com/kb/2383983/en-us.
Since you are going to demote the integration, you can also reverse the domain federated authentication settings for the other domain. For detailed information, please refer to Method 2 in the following KB article:
Users can no longer access Office 365 after you run the convert-MSOLDomaintoFederated cmdlet to convert an existing domain
http://support.microsoft.com/kb/2662960
Thanks,
Mindy Pan