That's 2 questions to be honest:
- Yes, BTC can be dethroned, "all" it takes is one of the other coins to explode into a much higher marketcap. With the recent dynamics since start of 2018, that is entirely possible within the next 12 months ;-)
- As for the price of BTC, I think a lot of that depends on how quickly things like SegWit and LN get active and used by most of the network. As long as that is not the case, the price will either slowly climb or remain as is. When it does get implemented and transaction costs/speeds improve, BTC price will be positively impacted.