When the TCU is reporting it no longre has a data connection, it may mean it can no longer connect to BMW. This may be because T-Mobile.de does not have a roaming agreement for Ireland. [ie you have No Service] I don't know how you turn off the warning.

You would not want to remove the TCU as you can use Navcoder to enable the Bluetooth and Voice control inside it.

You could try a PAYG SIM with a data connection, or try to turn off the peridic connection to BMW to report the cars' status and position.