The word "Alt-coin" should mean "Alternative Coins". And the word alternative in a layman's language should mean having an obvious option. Example, having an alternative plan means I can decide to use Plan B, most especially if plan A may not favour me at that time. Also, Coffee is an alternative to Tea, in this scenario, alternative is a choice and not a measure of importance. In a situation where an alternative is a choice, is therefore means that the Sorrow of one will be the pleasure of the alternative.
Relating this to cryptocurrency, if BTC who is the mother of Cryptocurrencies and who has gained extensive trust ceases to exist today, will altcoins flourish or will it make the people loose total interest in cryptocurrency.
if bitcoin has lost the trust of everyone then there are definitely no more cryptocurency users in the world. because bitcoin is the ICON of the world's cryptocurrency. Maybe many people don't know "altcoin" but everyone has heard the name "Bitcoin". so if bitcoin does not exist then cryptocurency will not exist.
There's no reason for altcoins to be in pleasure because once bitcoin loses its value, altcoins will definitely lose its value too. Yes, bitcoin is even more popular compared to altcoins and so people recognized bitcoin as the king of crypto while altcoins are only those coins used to become alternatives when they think bitcoin is not enough.
However, when the whole crypto market seems bullish because of bitcoin, eventually potential altcoins too will come up surging their prices. Only those altcoins with low potentials will remain undervalued.