>Would I lose everything I paid for?
I probably don't have access to over 95% of games I bought as physical copies 20 years ago and I don't know how many hard drives have given up on me over that time.
Valve and the contract you have with them is actually more durable than stuff physically lying around the house, it just doesn't feel that way because we don't have a good intuition about how brittle digital information stored on physical media is.