A new, "better" currency isn't going to displace Bitcoin overnight. It too will have to bootstrap an economy before it's viable. That's the hard part, and Bitcoin is already progressing towards it. And in the event a competitor comes along, you can always trade your Bitcoins for it.
I'm actually looking forward to Bitcoin competitors. It's the only way we are going to sort out the questions that constantly come up on the forum like "wouldn't it be better to have a constant rate of coin generation?" or "how can we remove the advantage that early adopters have?" or "why do we have to waste so much electricity?" These critics need to start writing code and prove that their solution is better by getting more people to adopt it.