No one knows and no one can predits on how long bitcoin will be alive and kicking in the market,though bitcoins dominates todays market this will not last foreverfor sure and new currency will defeat bitcoin
While in theory this seems correct at the same time bitcoin is showing no signs that is getting weaker, yes the bitcoin dominance has gotten lower in this year but it was impossible to maintain that bitcoin dominance for a long time since the amount of coins that has appeared and the amount of projects that have a really great concept and developers will slowly undermine bitcoin dominance but they are nowhere close to bitcoin and I do not think that is going to change anytime soon.
Replacing bitcoin on its position to the top would really be hard and it would really takes time but now we can already see the strong contestant for the future position but well we should not think off right now and the best thing to do is cherish the moments and money making with bitcoin.No one really knows on when bitcoin would able to last or would be replaced by other coin into its position.