you can't. on lost connection, the server Blazor instance hangs around for a little while waiting for a reconnect, but it exits as it don't know if the user will every reconnect. The client code just reloads the Blazor app if the Signal/R session can not reconnect.
if you need the Blazor app to recover from a Signal/R disconnect (and mobile browser are very aggressive at disconnecting, switching tabs will do it) you need to make the app recoverable. The app should save the state to a persistent store (server or local storage). on app load, it should check for the saved state and reset values. each page should check for saved state at init. it must also clear saved state (say when navigating away). a seamless recovery requires saving every keystroke, but this is pretty expensive.