Dear John
you are "misinterpreting" the situation. There is a general SAP maintenance strategy in place. EHS is part of ECC which is part of SAP ERP. SAP ERP is "maintained". What will happen 2020 nobody knows..
But there is an official place to look: This is SAP marketplace
So don't panic; in the past the situation was the same (with SAP 4.6, etc. etc.) and SAP delivered always a solution (e.g. may be we get SAP ERP 7.0 instead of 6.0).
C.B.