If no one use bitcoin today , Im really sure bitcoin price could be dump and sooner as it dump it might be dead if no one will use it for transaction. It bitcoin is dead. No one will still use it and other alt coins maybe affected too.
That's for sure to happen if all of us will totally ignore the usage of bitcoin and that is going to be like no use at all. And most of the people will look for some other things that can be useful for all of us, just like how we use bitcoin. Since bitcoin is the father of all crypto's for sure there is a domino effect to all alts if it will be dumped.
That depends. Other altcoins could just use fiat to determine the value of their coins when bitcoin is no more having its value. If there's no one using bitcoin doesn't mean the other altcoins will also failing. If the altcoins having such a strong communities that make them always using it then it will be fine. Although if bitcoin were dumped then the altcoin will be pumping, that's the natural law