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You are falsely conflating everyone switching ("nobody really cares about Bitcoin any more") with loss of marginal use cases (EG SatoshiDice and coffee). That's not how the substitution effect works. What actually happens those who gain the most value from Bitcoin stay and those who gain the least switch. That is basic economics.
When oil prices rise, we demand/produce/consume (IE substitute) more coal, nat gas, and alt energy instead. That doesn't mean nobody really cares about oil any more.
With a 1 MB blocksize limit one has 3 tps (reasonable practical estimate) for the current Bitcoin network. This translates into approximately 95 million transactions per year.
So here are some questions:
What non marginal use cases do you expect the average person to be able to use Bitcoin for?
Do you expect on average those transactions to be mined within that average person's life expectancy? That of their children? That of their grand children? That of their great grand children?
Please do the math.