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.
If you were just talking about your existing physical devices, depending on the brand and model most of them will be able to be used with a different hub. I know that’s a lot of work and it might not be something you want to consider, but in general the investment in the equipment itself can be salvaged if desired.