What happens if I ended subscription BUT NOT deleted an app with paid features activated?

You are not talking to Apple in these forums.

Some app developers offer permanent feature upgrades that you only pay for once. Those should stay active without a subscription. Such permanent features are becoming increasingly rare.

Others offer subscriptions for feature upgrades. Those need to be renewed by paying for the subscription for the features to stay active. Those features will be disabled or revert to their unpaid/free state if the subscription is not paid.

If you want to know about features in a specific app, you need to consult their documentation or web site, or contact the app developer.

Apple's weather app is free, they don't charge so whatever app you downlaoded and payed for is not an Apple product.

Again, you will need to contact the app developer and as kthem what happens when you stop the subscription.

Contact the app developer and ask them.

How to contact an app developer - Apple Support

If you are talking about Apple Music, you won’t be able to access music. The app will stay installed.

I had once with Lightroom that I forgot to charge my Apple ID. The subscription just ended, on the day that the payment was due

He means charge it up with money. A phone charger has nothing to do with the subject matter.