The software will continue work as long as Softmail remains in existence, but they may be skirting their license agreement. They are probably relying on the following clause for justification. In the excerpt below from the LTSC license agreement, the vendor (SoftMail.co.uk) is acting as the Customer, and its (primary) users are those to whom they are selling the software.
Roaming Rights
Customers with active Software Assurance for Office LTSC licenses can use Roaming Rights benefits. The single primary user of a licensed device can remotely access the software running on servers that the customer manages from a qualifying third-party device. They can also run the software in a virtual Operating System Environment (OSE) on a qualifying third-party device when they are not on the customer’s or their affiliates’ premises. Customers can host dedicated servers for this purpose in their own data centers or on servers that Authorized Outsourcers manage. A ‘qualifying third-party device’ refers to any device that you or your affiliates do not control, either directly or indirectly (for example, a third party’s public kiosk or an employee’s personal device). For example, an employee may not use their personal devices on premises and exercise their Roaming Rights benefits. This same user may access Office LTSC from this personal device when at home.
The 'primary user' is the individual who uses the licensed device more than 50 percent of 3 the time within any 90-day period. Non-primary users can also remotely access the software if they are using a device that has a license for the same version and edition of Office LTSC.