Ouch!
You could add one of the third-party dashboards, like actiontiles or sharptools. They are browser-based so they should continue to run. That would give you phone-based control of your existing devices, but you wouldn’t be able to add any new ones. You could create new rules through sharptools.
On the other hand, I can see not wanting to invest new money in the existing system.
SharpTools has a free tier which limits the total number of things you can do: I don’t know if it would meet your requirements or not.
In any case, one of those might give you time to move over to a new hub if you choose to do that. 
Here’s a recent discussion thread on the various dashboard options. As I said, I wouldn’t consider this a long-term option, you would have too many missing features, but it might give you some more time to figure out what to do.
Sharptools , actiontiles or native ST app for your wall panel? (2019)