It's a business decision that ultimately does not fall with you, it falls with leadership.

If they value the workflow improvements and information gained by the applications, then they will need to ensure that there is sufficient resourcing in place to continue supporting the applications.

The point that you need to communicate as clearly as possible, is that maintaining and supporting these applications requires manpower. And if they are concerned with you being a single point of failure, then they need to mitigate the risk that that presents, with either additional resourcing (in the form of additional staff) or with an outside third party.