The only reason there's analogue connectivity is due to back-compatibility with outdated systems (none physically present atm). Each hardware piece in our communication chain supports at least SIP, so that answers that. However, much like in every other large business machine, change is not always welcome, particularly if it involves expenditure of monetary resources. 
Appreciate your response.
I would make a global inventory and categorize on modem or non-modem analogue devices. If modem I would investigate wether they need to be as opposed to different solutions. That said in NL the use of modem devices at the moment is a thing of the past (10+ years ago with building management servers and stuff which I had to deal with which were connected to a physical Gateway).
That remains Fax/Analogue Phone devices. You could always plan a small project to migrate them to SIP. Not sure if there is any Cloud or IP-VPN situations where local devices need to connect to cloud, but even if this is the case and if there is many analogues you could for example go with an Audiocodes or a different solution connecting the analogue devices and even get some marginal resiliency connecting them to virtual MiVBs.
In my experience if you put in some time you might find out that you should be fine ditching the physical single point of failure gateways (hardware yikes) and migrate to a more robust centralized situation.
Change is hard for many. Start small and show it works and create some base of support. It might just sell itself. In current times I you don't want to be dependant on possible non-resilient hardware that can fail with non-resilient analogue stuff.
These days its not hard to migrate to SIP on a per port basis and in the end remotely phase out the physical Network elements.
My 2 cents and I hope the above is a bit the answer you were looking for.
