The price will only increase if there is demand. I think the existence of a single coin does not affect the price much. According to the simple rule of economics, the more buyers of a good, the more its price increases. Therefore, whether Bitcoin stands alone or not, it can proceed in a similar way.
There are many cryptocurrencies, but which one can you trust as much as Bitcoin? Your answer to this question will be similar to the answer you would give to the question asked in the topic.
in every market, competition is important to know the difference of their role. however, if there is no competition, i guess, people won't appreciate much about its existence.
and how people look at the demand factor may be different. so i guess, we won't really know the scenario for this.
or maybe, we will have a different competition, not among with cryptocurrencies but when it comes to holding various assets.
If bitcoin is the only cryptocurrency then the growth wouldn't be this high. We could've got its usage all around, and the acceptance level to be same as now as it had got value. In terms of growth we will at the days of 2015, because it is the altcoins that gave the competence and the growth shoot high. At some point Ethereum gave the hard competence, further the competence was found between Ethereum and Binance coin. Further it happened with XRP, so the competence keeps the market progressive and moving on the right track.