I just spoke with the head of the iRMT program, and here is the story:
They have been working on a COVID plan for some time now, and for the moment, all expiring certifications are extended until further notice.
In the not-too-distant future, the maintenance and service renewals will all be done ONLINE. The global infrastructure is currently being tested for this, and when it's ready to go live, upcoming renewals will be conducted online, and iRMT members will be advised accordingly. This is likely to start in Autumn of 2020. But for now, consider your iRMT expiry date has been extended.
As for the Heavy Maintenance, it's not practical to do renewals online (due to HM's more 'hands-on' nature). So current iRMT Heavy certificates will be extended farther into the future - probably for the next year at least.
There are plans to potentially hold limited 'social-distanced' physical training classes in certain 'bubbles' in countries that have been spared from heavy COVID outbreaks. But that depends on a lot of factors, as this pandemic is a long way from finished, and could actually get worse over the coming months. More information will be forthcoming as the situation develops!
But the important takeaway for iRMT certificate holders is: all expiring certifications are extended until further notice.