I'm a mechanical engineer that uses a variety of commercial software, as well as developing extensions for that software via the software's API, and also developing standalone software for our own internal purposes.
A lot of that commercial software that we use has a very long history, sometimes even starting way back in the mainframe days. It's expensive stuff, costing $100k or more per user.
A couple of programs follow the pure subscription model, and none of them follow the pay once to 'own', with a period of maintenance built into the purchase price.
What most of them follow is what I'll call a purchase and maintain model. The user purchases the software, then pays a yearly maintenance fee (typically 1/8 the purchase price) that provides regular updates and support (via phone and web portal) for as long as the maintenance fees are paid.
If the user stops paying maintenance, the then current version continues to be usable indefinitely, but the updates and support stop.
If the user decides to stop paying maintenance for a period of time, then wants to restart it, the user has to either 1) make all the maintenance back payments all the way back to when the payments stopped, or 2) , repurchase the software.
I don't know if any of that is useful to you, but it seems like you were trying to gather ideas on business models. I've spoken to some of the software companies that use this model, and they like it. They use it to make a rough internal allocation of resources/funds. The income from the maintenance fees covers the staff directly supporting end users, plus bug fixes. The income from the initial purchases funds strategic and tactical development of new functionally.
A final note: all of this often uses a floating license model with a central licensing server within the end users' controlling the number of simultaneous users (though a license file tied to particular computer(s) can be installed locally as an alternative). The users' company pays the yearly maintenance fee up front to get a licencing file that authorizes usage for the next 12 months. I don't see how this could work without running a licencing server, or across the internet, and that be more complicated than anything you want to consider.