Discovering that these Bitcoin wallets are unavailable as on your phone in the morning may be the result of a shut down by the developers or removal of the application from the app store that does hot mean that your Bitcoin in is gone as this depends on the wallet you use.
Your Bitcoin is not stored inside the application while using a non-custodial wallet you manage your keys and interact with the Bitcoin network through the help of the app.
Note that even if the application disappears, your Bitcoin remains recorded on the block chain.
You can restore access with the help of another compatible wallet with the availability of your recovery seed phrase or the valid private keys.

Custodian wallets however operate differently depending on the company that controls your privacy keys it access your funds recovery your Bitcoin may be managed if the service shuts down or faces financial problems.
Hence the choice of a wallet goes beyond it popularity or attractive interface.
One may inquire therefore if what happened to your funds should be put into consideration while choosing a Bitcoin if the developers abandon the project, or if you would have a significant focus on the simplicity of the application to use.